Fast Photo-carrier Multiplication by Engineered Potential Trap in MoS2/Ge Double Junction Phototransistor

Fast Photo-carrier Multiplication by Engineered Potential Trap in MoS2/Ge Double Junction Phototransistor | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Fast Photo-carrier Multiplication by Engineered Potential Trap in MoS2/Ge Double Junction Phototransistor Youngseo Park, Han Beom Jeong, Hu Young Jeong, Sangwan Sim, Geonwook Yoo, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7341136/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 08 Jan, 2026 Read the published version in Scientific Reports → Version 1 posted 15 You are reading this latest preprint version Abstract Broadband photodetectors in the visible and short-wave infrared wavelengths have garnered significant interest in recent years as a desirable method to achieve better detection in adverse weather conditions. Many material combinations have been proposed to replace expensive III-V based photodetectors; however, the photodetection performance of these novel material and device concepts showed undesirable performances due to uncontrollable charge-trap-based photomultiplication, preventing fast photoresponse and gain. To solve this issue, we devised an engineered potential trap in Ge/MoS 2 double junction phototransistor which show a high responsivity of 7.6 A/W (corresponding to an external quantum efficiency of 2,024%) as well as a fast photoresponse of 88.1 µs. The maximum photocurrent gain reaches 29.1 with broadband imaging capability. This excellent performance is achieved through photogenerated hole confined in p-Ge clad by MoS 2 and n-Ge induced multiple electrons, which diminished rapidly via recombination upon removal of illumination. Our device concept enables creation of highly sensitive fast broadband imaging based on mixed dimensional van der Waals heterojunctions. Physical sciences/Engineering Physical sciences/Materials science Physical sciences/Nanoscience and technology Physical sciences/Optics and photonics Physical sciences/Physics Photocurrent multiplication potential trap boradband photodetector SWIR van der Waals germanium MoS2 Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction The photodetection and visualization of short-wave infrared (SWIR) light ranging from 1 to 3 µm has garnered significant interest owing to the unprecedented advantages of high visibility in adverse weather and at night [ 1 – 5 ]. The lower Rayleigh scattering compared with the scattering of visible light owing to a longer wavelength allows a clear vision of haze. The SWIR light from nightglow facilitates night vision, including during dark moons. Hence, SWIR photodetection has been extensively utilized in various applications such as medical diagnostics [ 4 , 6 – 8 ], semiconductor inspection [ 3 , 4 ], astronomy [ 3 ], face recognition [ 9 ], and automotive [ 5 ]. Furthermore, broadband photodetection, which senses both visible and SWIR lights, is critical for compensating SWIR imaging. In automotives, for example, it is beneficial to render a color on SWIR imaging to identify traffic lights or road conditions [ 3 ]. To date, commercially available InGaAs photodiodes epitaxially grown on InP substrates have been predominantly employed for SWIR photodetection. However, the high material costs and limited responsivities of InGaAs photodiodes without carrier multiplications restrict their widespread usage in consumer products. Hence, various emerging materials such as graphene [ 10 , 11 ], quantum dots (QDs) [ 10 – 12 ], and black phosphorus [ 13 , 14 ] have been proposed for implementing highly responsive SWIR photodetectors in diverse device structures such as PN diodes [ 14 , 15 ], Schottky junction diodes [ 16 ], and field effect transistors (FETs) [ 11 – 13 , 17 ]. Furthermore, broadband photodetection has been demonstrated by adjoining a material with another material of a larger bandgap [ 18 , 19 ]. However, previous studies have relied on unintentionally present charge traps to obtain a photocurrent gain. A strong confinement of photogenerated carriers in the traps may result in a high responsivity; however, a slow response time is imminent owing to the uncontrollable delayed release of trapped charges. Ni et al. reported an ultrahigh responsivity of 10 9 A/W at a wavelength of 1450 nm in a Si QDs/graphene FET; however, its slow response time of 3.4 s is unfavorable for the aforementioned applications [ 11 ]. Achieving high responsivities and fast responses in photodetectors remains challenging. Herein, we present a high-performance broadband photodetector exhibiting fast photocarrier multiplication by embedding a potential trap formed by a Ge homojunction and a mixed-dimensional van der Waals (vdW) heterojunction (MoS 2 /Ge). The vdW heterojunctions of two-dimensional (2D) transition metal dichalcogenides (TMDCs) on conventional group IV or III–V semiconductors introduce more degrees of freedom to heterostructure band engineering because TMDCs can easily form heterojunctions via vdW forces regardless of the lattice constants [ 20 , 21 ]. The significant bandgap energy differences between TMDCs and semiconductor materials allow for creative band engineering to achieve broadband photodetectors [ 22 ], unlike previous attempts using bulk III–V heterojunctions. Moreover, double junctions consisting of vdW heterojunctions and homojunctions construct an engineered potential trap. While a prolonged stay of captured photocarriers in unintentionally present defect/interface trap results in an extremely slow response, the photocarriers in the engineered potential trap are instantly recombined upon removal of illumination, providing a high responsivity and a fast response time, simultaneously. Results and Discussion Device scheme In this study, we employed a MoS 2 /Ge vdW heterojunction a Ge homojunction to achieve broadband and ultrafast photodetection. The vdW heterojunction between MoS 2 and Ge exhibited broadband photodetection owing to a significant bandgap energy difference (Eg_MoS 2 : 1.4–2.2 eV [ 23 ]; Eg_Ge: 0.66 eV [ 24 ]). Moreover, in the n-Ge/p-Ge/MoS 2 double junction heterostructure, holes can be confined in the p-Ge region by tailoring the valence band. The accumulated photogenerated holes in the p-Ge lower the electron barrier between p-Ge and MoS 2 , resulting in a photocurrent gain and a high responsivity [ 25 , 26 ]. The engineered hole confinement, in contrast to unintentional charge traps, exhibits a rapid diminishment of trapped holes upon the removal of light, thereby maintaining a fast response time. A schematic illustration of the MoS 2 /Ge double junction phototransistor is shown in Fig. 1 a. The device is composed of a p-Ge/n-Ge homojunction and a p-Ge/n-MoS 2 heterojunction. The p-Ge shared by the two junctions is a base that serves as a hole confinement region. The n-MoS 2 and n-Ge functioned as an emitter and collector, respectively. A 100-nm-thick p-Ge was achieved via B-ion implantation on an n-Ge substrate, followed by fine etching in a dilute solution comprising NH 4 OH and H 2 O 2 (Figure S1 in Supporting Information). Prior to the transfer of the MoS 2 flake, the active area was defined by a circular opening with a diameter of 20 µm in an Al 2 O 3 layer. The details of the double junction phototransistor fabrication process and the optical image of the fabricated device are shown in Figure S2 (Supporting Information). The thickness of the transferred MoS 2 flakes was measured to be approximately 6.6 nm using atomic force microscopy (AFM), as shown in Fig. 1 b. The AFM image shows that the MoS 2 flakes uniformly coated the exposed p-Ge region. Raman spectroscopic measurements were performed on the MoS 2 /Ge vdW heterojunction. As shown in Fig. 1 c, three Raman peaks appeared at 300.8, 383.8, and 408.8 cm -1 , which corresponded to the Ge–Ge phonon mode in Ge [ 27 ], as well as the E12g and A1g phonon modes in MoS 2 [ 23 ], respectively. These results indicate the pristine quality of MoS 2 in the junction region after transfer. The interface of MoS 2 and Ge was characterized by a transmission electron microscopy (TEM) as shown in Fig. 1 d. A stack of multilayer MoS 2 was intact on the Ge, forming the heterojunction. Despite immediate transfer of MoS 2 after cleaning the Ge surface, a formation of a native oxide could not be avoided. Nonetheless, the very thin thickness of the native oxide, less than 2 nm, hardly affects carrier transport. The energy band diagram of Ge/MoS 2 double junction phototransistor was experimentally determined (see Fig. S3 and text in Supporting Information). To determine workfunctions the surface potentials of p-Ge, MoS 2 , and the p-Ge/MoS 2 junction were 0.47, 0.19, and 0.2 eV, respectively, as measured using kelvin probe force microscopy (KPFM). The indiscernible potential difference between MoS 2 and p-Ge/MoS 2 could be attributable to the relatively thick MoS2 (6 nm) in which the Ge underneath has little effect on the MoS 2 top surface. The bandgap energy of Ge was estimated using the Tauc plot to be 0.66 eV, which agrees with the value determined using electron energy loss spectroscopy (EELS) [ 18 ]. The bandgap energy of MoS 2 and electron affinities were derived from references [ 15 , 23 , 29 ]. At equilibrium, the energy band diagram of the MoS 2 /p-Ge/n-Ge heterojunction reveals a staggered-gap (type II) at MoS 2 /p-Ge. A conduction band offset and a valence band offset of 0.6 eV and 1.44 eV, respectively, were estimated. The carrier transport and amplification mechanism in the device can be understood in terms of the resulting energy band diagram, as shown in Fig. 1 e. The significant bandgap difference between Ge and MoS 2 contributed primarily to a high energy barrier to holes in the p-Ge instead of a conduction band offset in the heterojunction. Such dissimilar energy barriers in the heterojunction enabled MoS 2 to function as an ideal emitter, where more electrons from MoS 2 were transferred to p-Ge than holes from p-Ge to MoS 2 [ 30 ]. The hole current injected via the p-Ge considered as a base would not propagate to MoS 2 (emitter); as such, electrons were induced from the emitter efficiently. The induced electrons were transported over the base and collected by the n-Ge, which is known as a collector. When the device functions as a photodetector, a positive bias is applied to the n-Ge with respect to the emitter (MoS 2 ), while the base (p-Ge) remains open. Hence, the base–emitter (p-Ge/n-MoS 2 ) is forward biased, whereas the base–collector (p-Ge/n-Ge) is reverse-biased. The potential of the base should be determined by equalizing the current across each heterojunction; therefore, the bias is primarily allocated to the reverse bias of the base–collector junction, as denoted by the black lines in the figure. When light is incident on n-MoS 2 , visible light is primarily absorbed in the MoS 2 region, and SWIR light transparent to the MoS 2 is absorbed by Ge. Electrons and holes are photogenerated across the emitter–base heterojunction transport to the emitter and base, respectively. The electrons in the emitter flows out to the contact, but the holes are confined in the base. Hence, the accumulation of holes in the base lowers the energy barriers, particularly in the emitter–base heterojunction, thereby resulting in an injection of electrons from the emitter to the base, followed by a drift of electrons to the collector. As such, one photogenerated hole can induce more than one electron, enabling a high responsivity exceeding 100% external quantum efficiency (EQE). Electrical characterization Electrical measurements were performed on an n-MoS 2 /p-Ge/n-Ge double junction phototransistor under dark conditions at room temperature. First, the p-Ge (base, B)/n-MoS 2 (emitter, E) heterojunction and p-Ge (B)/n-Ge (collector, C) homojunctions were separately characterized. Under a voltage swept from − 4 to 4 V, current rectifying behaviors were clearly observed at both p–n junctions, as shown in Fig. 2 a. The ON/OFF current ratios (I ON /I OFF ) of the B–E and B–C junctions were approximately 2.9×10 7 and 1.5×10 3 , respectively. Saturation current in p-Ge/n-Ge homojunction was much higher than that in p-Ge/n-MoS 2 heterojunction because of germanium’s narrow bandgap and a larger junction area of B-E junction (314 µm 2 ) compared to that of B-C junction (11,309 µm 2 ). The ideality factor ( n ) was estimated from the plot of ln( I ) vs. V , and the values were 1.21 and 1.05 for the p-Ge/n-MoS 2 heterojunction and p-Ge/n-Ge junction, respectively. The slight deviations from the ideal diode can be ascribed to interface defects at the junction or additional series resistance [ 31 , 32 ]. Figure 2 b shows the input characteristics ( I B – V BE , where I B and V BE are the base current and base–emitter voltage, respectively) of the device with different V CB biases. As observed in a forward-biased p–n junction, I B increased exponentially with V BE . As V CB increased, I B decreased and then rapidly saturated, implying that I B is independent of the band shape above V CB = 0.15 V because the reverse current of the base–collector junction had saturated. The output characteristics ( I C – V CE , where I C and V CE are the collector current and collector–emitter voltage, respectively) in the common-emitter mode were measured at I B at steps of 200 nA, as shown in Fig. 2 c. It was observed that the input base current amplified under a V CE of > ~ 3.5 V. At low V CE values, it was insufficient to tunnel the native oxide of Ge and lower the potential barrier on the B–E junction owing to the difference in resistance between the B–E and B–C junctions. Hence, I C increased exponentially after a sufficient V CE was applied. Figure 2 d shows the combined plot of I B and I C vs. V BE , which is known as the Gummel plot. The common-emitter current gain ( β ), defined as I C / I B , is shown on the right axis in the figure. As V BE increased, both I B and I C increased exponentially in general. The β at V BE ˃ 1 V was distinct because the non-ideal recombination current at a low V BE did not increase I C . To the best of our knowledge, a maximum β value of approximately 29, which is the highest value recorded among 2D and three-dimensional (3D) vdW junction devices, has been reported. As V BE increased further, the increase in I C declined compared with that of I B , and β diminished. This contributed to a high-level injection and series resistance, resulting in a simultaneous slope-over in both the I B and I C , as shown in the figure. The electrical performance of the device was compared with those of previously reported hot electron transistors and heterojunction bipolar transistors based on 2D materials in terms of β and the collector current density ( J C ). As shown in Figure S5, the n-MoS 2 /p-Ge/n-Ge double junction phototransistor exhibited the highest J C along with a decently high β . Devices such as photodetectors exploit these favorable performances, such as a high β to amplify photo-induced holes in the base region, which will be discussed below. Additionally, MoS 2 /Ge double junction devices can be potentially deployed as electrical devices (e.g., switches and amplifiers). Photoresponse characteristics The photoresponse of the n-MoS 2 /p-Ge/n-Ge double junction phototransistor was characterized by illuminating either a visible (466 nm) or SWIR (1550 nm) laser at room temperature. A positive V CE was applied to the device with an open base, while maintaining the n-MoS 2 (E)/p-Ge (B) junction in forward bias and the p-Ge (B)/n-Ge (C) junction in reverse bias. Because the base is opened, the base current is governed by thermal generation in the dark and photogeneration in light. Figure 3 a shows the I C – V CE curves under 466 and 1550 nm illumination under the same optical irradiance of 10 mW/cm 2 on a linear scale, and the inset shows the I C – V CE curves on a semi-logarithmic scale. An increase in I C was observed for both the 466 and 1550 nm illuminations. Despite the lower photon energy of the 1550 nm light, which implies a higher number of incident photons at the same irradiance, the photoresponse of the 466 nm light was greater than that of the 1550 nm light. Because of the long penetration depth of 20 µm for the 1550 nm light in Ge [ 33 ], all the lights at 1550 nm were not absorbed in the p-Ge, whereas incident light was partially absorbed at the p-Ge/n-Ge junction. Subsequently, the time-resolved photocurrent ( I ph ) was characterized based on optical incident powers of 1, 3, 10, 30, 100, 300 and 1000 mW/cm 2 (Figure S6 in Supporting Information). The light modulated at a frequency of 1 kHz was illuminated on the device with a V CE of 4 V. When the incident light power increased, the photocurrent increased linearly with a slope of 1.01 and 0.93 under 466 and 1550 nm illuminations, respectively, as shown in Figure S6b and d. For a more quantitative analysis of the response time, the transient photocurrent responses of the 466 and 1550 nm light were normalized, as shown in Fig. 3 b. The response time ( t r ) is defined as t r = ( t rise + t fall ) /2, where t rise is the rising time when the light is “on,” and t fall is the falling time when the light is “off.” For 466 nm laser modulation, the t rise and t fall were estimated to be 202.3 µs and 88.1 µs, respectively, giving rise to the tr of 145 µs. Under the illumination of the 1550 nm laser, a tr of 224 µs was obtained based on t rise and t fall of 214.9 and 232.8 µs, respectively. The extracted response times were limited by the maximum sampling rate of 110 µs, and the actual response speed was expected to be higher. The specific detectivity ( D *) is defined as D * = R × ( A · BW ) 1/2 / i n , where R is the responsivity, A is the area, BW is the bandwidth, and i n is the measured noise current. D * can be estimated by assuming that the shot noise is dominant. The shot noise can be expressed as i n = (2· e · I d · BW ) 1/2 , where e is the electron charge, and I d is the dark current. However, non-Ohmic contacts on the 2D materials and fluctuation of carrier transport over the vdW heterojunction may result in dominant noise components. For an accurate estimation of D *, the noise power spectral density (NPSD) of the dark current was measured at various V CE values, as shown in Figure S7 (Supporting Information). The NPSD curves for all biases indicated a 1/f dependence. A considerable increase in the spectral noise density as V CE increased was observed. A frequency of 60 Hz and its harmonics were not the intrinsic noise of the device; instead, they originated from the 60 Hz power line. The noise currents with a BW of 1 kHz when V CE were 1 and 4 V were 1.01×10 –11 and 9.92×10 –10 A/Hz 0.5 , respectively. Figure 3 c and d show the responsivity, EQE, and resulting D * vs. V CE for visible and SWIR lights, respectively (see calculation details in the Methods section). As V CE increased, R and EQE increased linearly and reached maximum values of 7.6 A/W and 2,024%, respectively, for the 466 nm laser. Meanwhile, under the 1550 nm laser illumination, R and EQE increased at V CE >0.5 V owing to the potential barrier of the B–E junction and the absence of photogenerated carriers in MoS 2 , reaching maximum values of 4.7 A/W and 376%, respectively. Despite the increase in responsivity at higher V CE values at all detection ranges, the detectivity remained relatively constant because the noise current increased simultaneously. The maximum detectivities were 1.85×10 8 and 8.01×10 7 Jones under the 466 and 1550 nm illuminations, respectively. The detectivity was calculated by removing the input power noise (observed at intervals of 60 Hz, as shown in Figure S7). The detectivity was relatively low due to the high noise current caused by the high dark current. Additionally, Figure S8 shows the spectral responsivity and external quantum efficiency of the Ge/MoS 2 double junction phototransistor, confirming its broadband detection capability from visible to SWIR wavelengths via photocurrent amplification. Photocurrent multiplication in the n-MoS 2 /p-Ge/n-Ge double junction phototransistor was directly evidenced by a comparison with the photoresponses of the p-Ge/n-MoS 2 heterojunction and p-Ge/n-Ge homojunction under 466 and 1550 nm illumination (Figs. 3 e and f). Under the 466 nm illumination, the photocurrents (EQE) when the bias voltage was 4 V were 2.96×10 − 7 A (69.7%) and 1.54×10 − 7 A (36.2%) in the p-Ge/n-Ge homojunction and p-Ge/n-MoS 2 heterojunction, respectively, which indicate EQE values of less 100% (Fig. 3 e). Meanwhile, the photocurrent (EQE) in the double junction phototransistor was 8.15×10 − 6 A (1,918.8%) at V CE = 4 V, which implies that the photoresponse gain was present. The photocurrent gain ( β ph ) of the double junction phototransistor, as calculated for 466 and 1550 nm illuminations, is shown in Fig. 3 g. At higher bias voltages, β ph reached the maximum measured values, i.e., 29.1 and 11.6 for 466 and 1550 nm, respectively, and these values were similar to the base current gain obtained in the aforementioned electrical characterization. For photodetectors and image sensors, responsivity and response speed are critical figures-of-merit. To detect weak light in an image sensor, the photodetector must have both a fast response time and a high responsivity. Figure 4 shows the cut-off frequencies and responsivities of several previously reported broadband photodetectors. Without photocurrent gain, devices exhibit a rapid response time because carriers are photogenerated and then promptly vanish in response to the on/off of light [ 14 , 15 , 17 ]. On the other hand, in the devices with a high responsivity due to photocurrent gain, photogenerated carriers do not completely disappear when the light is switched off, resulting in a long response time [ 11 – 13 ]. In other words, it has been challenging to develop desirable features in both. It is worth noting that our phototransistor outperformed other photodetectors in terms of response time and responsivity. This capability is credited with broadband imaging, including SWIR for night vision and harsh environments in self-driving. Additionally, the broadband imaging capability of our device was investigated. Figure 5 a shows a schematic diagram of the measurement systems used for broadband imaging. A smile image, which was mounted onto the XY-axis motorized stage, was placed between the light source and lens. The light incident from the 466 and 1550 nm lasers was focused onto the phototransistor via the lens after it passed through the object. Visible/SWIR smile images of 32 × 32 pixels are clearly depicted in Figs. 5 b–c. These results imply that the device proposed herein can be utilized as a broadband imaging sensor from the visible to SWIR light range. Conclusions In this study, we demonstrate a MoS 2 /Ge double junction phototransistor and investigated its electrical and photoresponse characteristics. The electrical properties obtained demonstrated their potential as an electronic device and a photodetector with β = 29. The MoS 2 /Ge phototransistor allowed broadband detection from the visible to SWIR wavelength range. The double junction phototransistor exhibited high photocurrent amplification, with β ph = 29.1 (11.6) at 466 (1550) nm. Moreover, the fabricated phototransistor exhibited a high responsivity of 7.4 (4.7) A/W and fast t rise ( t fall ) of 202.3 (214.9) and 88.1 (232.8) µs, respectively, under a 466 (1550) nm illumination. The fast broadband photodetection demonstrated in this study, which was achieved by utilizing a heterogeneously integrated Ge/TMDC structure, will greatly facilitate bringing improved photodetectors to the market, such as an eye safe detector operating in the 1550 nm wavelength as opposed to the harmful 940 nm wavelength, or sensors that allow to obtain clear visibility in adverse weather conditions. The concept of a vdW Ge/TMDC heterojunction addition to conventional homojunction device can be adopted to improve the performance of many conventional III–V devices that operate with inferior fundamental operations that limit their performances with much cheaper cost. The 2D/3D heterostructure concept demonstrated here removes this bottleneck, thereby providing opportunities for the development of ultrahigh-performance electric and optoelectronic devices. Methods Material characterization Morphology was measured using AFM (XE100, Park Systems) in non-contact mode. Kelvin probe force microscopy measurement was performed using AFM (XN-10, Park Systems) in non-contact mode. Micro-Raman spectroscopy measurements (LabRam HR Evolution, Horiba) of the Ge/MoS 2 double junction phototransistor were performed based on a spatial resolution of 1 µm and a 532 nm excitation laser under ambient conditions. The sample for TEM analysis was prepared using a focused ion beam system (Quanta 3D FEG, FEI). TEM was performed using a high-resolution TEM (JEM-2100F, JEOL) with an operating voltage of 200 kV. Electrical and optoelectrical measurements Electrical and optoelectrical characteristic measurements were performed using a semiconductor parameter analyzer (4200A-SCS, Keithley Instruments) with 466 and 1550 nm diode pumped solid-state lasers (Civil laser). The transient characteristics were measured using a source meter (2614 B, Keithley Instruments) with pulsed 466 and 1550 nm lasers. The spectral responsivities were measured using monochomater (MonoRa200, Dongwoo Optron) with Xenon lamp. The NPSDs were measured at a sampling rate of 1,600 Hz under dark conditions using a dynamic signal analyzer (35670A, Agilent). Response speed, responsivity, detectivity, and photocurrent gain extraction The t rise and t fall were defined as the time intervals that increased from 10–90% at the peak values and decreased from 90–10%, respectively. To extract the responsivity, the photocurrent was calculated as I ph = I light - I dark , where I light is the measured current with illuminations of various power intensities and wavelengths, and I dark is the measured current under dark conditions. The responsivity was calculated as R = I ph / P in , where I ph and P in are the photocurrent and incident optical power, respectively. To characterize in, the measured current NPSD was square-rooted and integrated by the BW , where BW is the specified bandwidth. The noise equivalent power (NEP) of our device was calculated as NEP = i n / R , where in is the total noise current in units of A·Hz -0.5 . The detectivity is expressed as D * = A -0.5 /NEP, where A is the area of the heterojunction phototransistor. The photocurrent gain was extracted as β ph = I ph,tr / I ph,pn , where I ph,tr is the photocurrent of the vdW Ge/MoS 2 heterojunction phototransistor, and I ph,pn is the photocurrent of the p–n junctions. Declarations ASSOCIATED CONTENT Supporting Information Include details about the fabrication process, characterization of the energy band diagram, comparison of electrical performance, and additional optoelectronic characteristics (PDF) AUTHOR INFORMATION Corresponding Author *Junseok Heo - Department of Electrical and Computer Engineering, Ajou University, Suwon 16499, South Korea; Email: [email protected] Author Contributions Y.P. fabricated the devices and performed the electrical and optical measurements. H.B.J and H.Y.J performed the material characterizations. Y.P., S.S., and J.H. analyzed the experiments and wrote the manuscript. All authors contributed to the discussion and analysis of the results of the manuscript. J.H. supervised the project. Notes The authors declare no competing interests. FUNDING This study was supported by the National R&D Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (RS-2024-00438811, RS-2025-00564261, RS-2025-02217113). Data Availability The datasets used and/or analysed during the current study available from the corresponding author on reasonable request. References Naboulsi, M. A. Fog attenuation prediction for optical and infrared waves. Opt. Eng. 43 (2), 319. 10.1117/1.1637611 (2004). Driggers, R. G., Hodgkin, V. & Vollmerhausen, R. What good is SWIR? Passive day comparison of VIS, NIR, and SWIR. Infrared Imaging Syst. Des. Anal. Model. Test. XXIV . 8706 , 87060L. 10.1117/12.2016467 (2013). Martin, T., Brubaker, R., Dixon, P., Gagliardi, M. A. & Sudol, T. 640x512 InGaAs focal plane array camera for visible and SWIR imaging, in Infrared Technology and Applications XXXI , May vol. 5783, p. 12, (2005). 10.1117/12.603406 Malchow, D., Battaglia, J., Brubaker, R. & Ettenberg, M. High speed short wave infrared (SWIR) imaging and range gating cameras, in Thermosense XXIX , Apr. vol. 6541, p. 654106, (2007). 10.1117/12.721747 Bernini, N., Bertozzi, M., Cerri, P. & Fedriga, R. I. SWIR Cameras for the Automotive Field: Two Test Cases, ISRN Automot. Eng. , vol. pp. 1–11, Apr. 2014, (2014). 10.1155/2014/858979 Tsuboi, S. & Jin, T. Shortwave-infrared (SWIR) fluorescence molecular imaging using indocyanine green-antibody conjugates for the optical diagnostics of cancerous tumours, RSC Adv. , vol. 10, no. 47, pp. 28171–28179, Jul. (2020). 10.1039/d0ra04710d Qi, J. et al. Real-Time and High-Resolution Bioimaging with Bright Aggregation-Induced Emission Dots in Short-Wave Infrared Region, Adv. Mater. , vol. 30, no. 12, Mar. (2018). 10.1002/adma.201706856 Yu, Z. et al. High-Resolution Shortwave Infrared Imaging of Vascular Disorders Using Gold Nanoclusters. ACS Nano . 14 (4), 4973–4981. 10.1021/acsnano.0c01174 (2020). Narang, N. & Bourlai, T. Face recognition in the SWIR band when using single sensor multi-wavelength imaging systems. Image Vis. Comput. 33 , 26–43. 10.1016/j.imavis.2014.10.005 (2015). Goossens, S. et al. Broadband image sensor array based on graphene-CMOS integration. Nat. Photonics . 11 (6), 366–371. 10.1038/nphoton.2017.75 (2017). Ni, Z. et al. Plasmonic Silicon Quantum Dots Enabled High-Sensitivity Ultrabroadband Photodetection of Graphene-Based Hybrid Phototransistors. ACS Nano . 11 (10), 9854–9862. 10.1021/acsnano.7b03569 (2017). Kufer, D. et al. Hybrid 2D-0D MoS2-PbS quantum dot photodetectors. Adv. Mater. 27 (1), 176–180. 10.1002/adma.201402471 (2015). Cao, R. et al. Black Phosphorous/Indium Selenide Photoconductive Detector for Visible and Near-Infrared Light with High Sensitivity. Adv. Opt. Mater. 7 (12), 1–7. 10.1002/adom.201900020 (2019). Ye, L., Li, H., Chen, Z. & Xu, J. Near-Infrared Photodetector Based on MoS2/Black Phosphorus Heterojunction. ACS Photonics . 3 (4), 692–699. 10.1021/acsphotonics.6b00079 (2016). Geum, D. M. et al. Arrayed MoS2–In0.53Ga0.47As van der Waals Heterostructure for High-Speed and Broadband Detection from Visible to Shortwave-Infrared Light. Small 10.1002/smll.202007357 (2021). Heves, E. & Gurbuz, Y. Highly Responsive, Solution-Based Al/PbS and Au-Ti/PbS Schottky Photodiodes for SWIR Detection, 14 , 3, pp. 816–820, (2014). Kim, S. G. et al. Infrared Detectable MoS2 Phototransistor and Its Application to Artificial Multilevel Optic-Neural Synapse. ACS Nano . 13 (9), 10294–10300. 10.1021/acsnano.9b03683 (2019). Hwang, A. et al. Visible and infrared dual-band imaging via Ge/MoS2van der Waals heterostructure. Sci. Adv. 7 (51), 1–9. 10.1126/sciadv.abj2521 (2021). Lee, C. H. et al. Design of p-WSe 2 /n‐Ge Heterojunctions for High‐Speed Broadband Photodetectors. Adv. Funct. Mater. 2107992 , 2107992. 10.1002/adfm.202107992 (2021). Choi, W. et al. Recent development of two-dimensional transition metal dichalcogenides and their applications. Mater. Today . 20 (3), 116–130. 10.1016/j.mattod.2016.10.002 (2017). Lopez-Sanchez, O. et al. Light generation and harvesting in a van der waals heterostructure. ACS Nano . 8 (3), 3042–3048. 10.1021/nn500480u (2014). Park, Y., Hwang, A. J., Lee, C., Yoo, G. & Heo, J. Broadband photodetection of MoS2/p-Ge/n-Ge bipolar heterojunction phototransistor, in Conference on Lasers and Electro-Optics, CLEO 2021 - Proceedings , 2021, p. STh5B.3, 2021, p. STh5B.3, (2021). 10.1364/cleo_si.2021.sth5b.3 Zhao, Z. Y. & Liu, Q. L. Study of the layer-dependent properties of MoS2 nanosheets with different crystal structures by DFT calculations. Catal. Sci. Technol. 8 (7), 1867–1879. 10.1039/c7cy02252b (2018). Trommer, J. et al. Enabling Energy Efficiency and Polarity Control in Germanium Nanowire Transistors by Individually Gated Nanojunctions. ACS Nano . 11 (2), 1704–1711. 10.1021/acsnano.6b07531 (2017). Su, B. W. et al. A gate-tunable symmetric bipolar junction transistor fabricated: Via femtosecond laser processing, Nanoscale Adv. , vol. 2, no. 4, pp. 1733–1740, Apr. (2020). 10.1039/d0na00201a Li, H., Ye, L. & Xu, J. High-Performance Broadband Floating-Base Bipolar Phototransistor Based on WSe2/BP/MoS2 Heterostructure. ACS Photonics . 4 (4), 823–829. 10.1021/acsphotonics.6b00778 (2017). Prucnal, S. et al. Superconductivity in single-crystalline aluminum- and gallium-hyperdoped germanium. Phys. Rev. Mater. 3 (5), 1–10. 10.1103/PhysRevMaterials.3.054802 (2019). Lee, C. et al. Anomalous lattice vibrations of single- and few-layer MoS2. ACS Nano . 4 (5), 2695–2700. 10.1021/nn1003937 (2010). Nishimura, T., Luo, X., Matsumoto, S., Yajima, T. & Toriumi, A. Almost pinning-free bismuth/Ge and /Si interfaces. AIP Adv. 9 (9). 10.1063/1.5115535 (2019). Anderson, B. & Anderson, R. Fundamentals of Semiconductor Devices . McGraw-Hill College; 1st edition, (2004). Choudhary, N. et al. Two-dimensional lateral heterojunction through bandgap engineering of MoS2 via oxygen plasma. J. Phys. Condens. Matter . 28 (36). 10.1088/0953-8984/28/36/364002 (2016). Yan, X. et al. High Performance Amplifier Element Realization via MoS2/GaTe Heterostructures. Adv. Sci. 5 (4), 1–7. 10.1002/advs.201700830 (2018). Eng, P. C., Song, S. & Ping, B. State-of-the-art photodetectors for optoelectronic integration at telecommunication wavelength, Nanophotonics , vol. 4, no. 1. Walter de Gruyter GmbH, pp. 277–302, Jan. (2015). 10.1515/nanoph-2015-0012 Additional Declarations No competing interests reported. Supplementary Files SupportingInformation250720.docx Cite Share Download PDF Status: Published Journal Publication published 08 Jan, 2026 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 04 Nov, 2025 Reviews received at journal 22 Oct, 2025 Reviews received at journal 19 Oct, 2025 Reviewers agreed at journal 19 Oct, 2025 Reviews received at journal 17 Oct, 2025 Reviewers agreed at journal 14 Oct, 2025 Reviewers agreed at journal 13 Oct, 2025 Reviewers agreed at journal 12 Oct, 2025 Reviews received at journal 07 Sep, 2025 Reviewers agreed at journal 22 Aug, 2025 Reviewers invited by journal 18 Aug, 2025 Editor assigned by journal 18 Aug, 2025 Editor invited by journal 18 Aug, 2025 Submission checks completed at journal 13 Aug, 2025 First submitted to journal 13 Aug, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7341136","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":504051507,"identity":"2f2afbd7-5124-4b80-b80d-f884a3c6a577","order_by":0,"name":"Youngseo Park","email":"","orcid":"","institution":"Ajou University","correspondingAuthor":false,"prefix":"","firstName":"Youngseo","middleName":"","lastName":"Park","suffix":""},{"id":504051508,"identity":"95577f5a-33ea-4c9c-a1d0-f4cae506c434","order_by":1,"name":"Han Beom Jeong","email":"","orcid":"","institution":"Korea Advanced Institute of Science and Technology (KAIST)","correspondingAuthor":false,"prefix":"","firstName":"Han","middleName":"Beom","lastName":"Jeong","suffix":""},{"id":504051510,"identity":"9daa7b27-396f-4953-87a2-efb47ef15b7e","order_by":2,"name":"Hu Young Jeong","email":"","orcid":"","institution":"Ulsan National Institute of Science and Technology (UNIST)","correspondingAuthor":false,"prefix":"","firstName":"Hu","middleName":"Young","lastName":"Jeong","suffix":""},{"id":504051512,"identity":"89480764-b982-4581-8c3d-4e0627a6c15f","order_by":3,"name":"Sangwan Sim","email":"","orcid":"","institution":"Hanyang University","correspondingAuthor":false,"prefix":"","firstName":"Sangwan","middleName":"","lastName":"Sim","suffix":""},{"id":504051517,"identity":"5f13aa0b-bb74-482d-84b4-d4371d33f796","order_by":4,"name":"Geonwook Yoo","email":"","orcid":"","institution":"Soongsil University","correspondingAuthor":false,"prefix":"","firstName":"Geonwook","middleName":"","lastName":"Yoo","suffix":""},{"id":504051518,"identity":"142bdbb5-3eed-4d07-af42-62559c4bdb4b","order_by":5,"name":"Junseok Heo","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAxElEQVRIiWNgGAWjYBACxgYeIFnBwAzlJxCr5QwpWhgYgFoY2+A8IrQw9589+ODjPDt2fokExg8/GNLyCTtsRl6y4cxtycySMxKYJXsYciwbCGvhMZPm3cbMbHAjgUEaGBAGhG3pP2P+m3dOPUgL82/itDTkmDHzNhwGaWED2pJDhJYZOcaSM44dB/rjYZtlj0EaYS2G/WcMP3yoqU7mZ08+fONHRTIRWhogdDLIjQwMhDUwMMhDaTsi1I6CUTAKRsFIBQAVDzPuORZDfAAAAABJRU5ErkJggg==","orcid":"","institution":"Ajou University","correspondingAuthor":true,"prefix":"","firstName":"Junseok","middleName":"","lastName":"Heo","suffix":""}],"badges":[],"createdAt":"2025-08-10 23:38:14","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7341136/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7341136/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-026-35134-z","type":"published","date":"2026-01-08T15:59:10+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":90298350,"identity":"39e4c9d3-b85f-4d60-b04f-21c00d4d5faf","added_by":"auto","created_at":"2025-09-01 08:45:55","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1379016,"visible":true,"origin":"","legend":"\u003cp\u003eCharacterizations and operating principle of Ge/MoS\u003csub\u003e2\u003c/sub\u003e double junction phototransistor. (a) Schematic diagram of Ge/MoS\u003csub\u003e2\u003c/sub\u003e double junction phototransistor. (b) Atomic force microscopy image of Ge/MoS\u003csub\u003e2\u003c/sub\u003e heterojunction. Inset shows MoS\u003csub\u003e2\u003c/sub\u003e thickness corresponding to dashed green arrow. (c) Raman spectra for Ge/MoS\u003csub\u003e2\u003c/sub\u003e vdW heterojunction. (d) Cross-sectional TEM image. (e) Band structure of Ge/MoS\u003csub\u003e2\u003c/sub\u003e double junction phototransistor under dark condition and illumination.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-7341136/v1/b0c2907b2dbc2a2ceb7b26b0.png"},{"id":90298345,"identity":"ac5edf65-5c42-499d-ab84-bd7a8e7d7418","added_by":"auto","created_at":"2025-09-01 08:45:55","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":262779,"visible":true,"origin":"","legend":"\u003cp\u003eElectrical characteristics of the fabricated device. (a) \u003cem\u003eI\u003c/em\u003e–\u003cem\u003eV\u003c/em\u003e characteristics of p-Ge/n-Ge homojunction and p-Ge/n-MoS\u003csub\u003e2\u003c/sub\u003e heterojunction. Inset shows circuit schematics for measurements of p–n junctions. (b) Input characteristics for various \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e and (c) output characteristics under different \u003cem\u003eI\u003c/em\u003e\u003csub\u003eB\u003c/sub\u003e of Ge/MoS\u003csub\u003e2\u003c/sub\u003e double junction transistors. Insets show circuit schematics for measurements of double juntion transistors. (d) Gummel plot of Ge/MoS\u003csub\u003e2\u003c/sub\u003e double junction transistor with corresponding current gain (\u003cem\u003eβ\u003c/em\u003e).\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-7341136/v1/9dc9c421e6bbe70c077889e4.png"},{"id":90300105,"identity":"e49f175a-70d8-4f06-adc7-c5ac9ce22f36","added_by":"auto","created_at":"2025-09-01 08:53:55","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":333577,"visible":true,"origin":"","legend":"\u003cp\u003ePhotoresponse characteristics of Ge/MoS\u003csub\u003e2\u003c/sub\u003e double junction \u0026nbsp;phototransistor. (a) \u003cem\u003eI\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e–\u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e characteristics in dark condition and under 466 and 1550 nm illuminations of 10 mW/cm\u003csup\u003e2\u003c/sup\u003e on linear scale. Inset shows \u003cem\u003eI\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e–\u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e curves on semi-logarithmic scale. (b) Time-resolved photoresponse characteristics to pulsed 466 and 1550 nm lasers with frequency of 20 Hz. Insets show rising times and falling times under 466 and 1550 nm illuminations. Detectivity (\u003cem\u003eD\u003c/em\u003e*), responsivity (\u003cem\u003eR\u003c/em\u003e), and external quantum efficiency (EQE) under (c) 466 nm and (d) 1550 nm illuminations of 10 mW/cm\u003csup\u003e2\u003c/sup\u003e. Photocurrent vs. bias voltage of p-Ge/n-Ge homojunction, p-Ge/n-MoS\u003csub\u003e2\u003c/sub\u003e heterojunction, and Ge/MoS\u003csub\u003e2\u003c/sub\u003e double junction phototransistor under (e) 466 and (f) 1550 nm illumination of 10 mW/cm\u003csup\u003e2\u003c/sup\u003e. (g) Photocurrent gain (\u003cem\u003eβ\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e) vs. \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e for double junction phototransistor.\u0026nbsp;\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-7341136/v1/3099d58c93761ab02860dfaa.png"},{"id":90298346,"identity":"523a103a-94a6-4e65-8550-677a90b05e37","added_by":"auto","created_at":"2025-09-01 08:45:55","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":26378,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of frequency vs. responsivity of Ge/MoS\u003csub\u003e2\u003c/sub\u003e double junction phototransistor and several photodetectors for broadband detection. Dashed horizontal line indicates frequency of 200 Hz, and dashed vertical line indicates 100% EQE (1.24 A/W for 1,550 nm light).\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-7341136/v1/fa37fb640a99f57051e835be.png"},{"id":90298351,"identity":"dc816401-e7d8-4d6d-91e4-766563a62a00","added_by":"auto","created_at":"2025-09-01 08:45:55","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":917920,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic diagram of measurement systems used for broadband imaging. Inset shows the object. Smile images detected under (b) 466 and (c) 1550 nm illuminations.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-7341136/v1/456e41da58b37c23980c8e97.png"},{"id":100069425,"identity":"2bac82e9-07ba-4106-91c3-f9064ffa672e","added_by":"auto","created_at":"2026-01-12 16:13:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3448003,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7341136/v1/9782873f-809e-454b-bb70-68477fff8cd3.pdf"},{"id":90300107,"identity":"bbca55f7-c1e2-4410-9189-8293cc816b81","added_by":"auto","created_at":"2025-09-01 08:53:55","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":2993836,"visible":true,"origin":"","legend":"","description":"","filename":"SupportingInformation250720.docx","url":"https://assets-eu.researchsquare.com/files/rs-7341136/v1/697feaea3a82dd7e13db209b.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Fast Photo-carrier Multiplication by Engineered Potential Trap in MoS2/Ge Double Junction Phototransistor","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe photodetection and visualization of short-wave infrared (SWIR) light ranging from 1 to 3 \u0026micro;m has garnered significant interest owing to the unprecedented advantages of high visibility in adverse weather and at night [\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. The lower Rayleigh scattering compared with the scattering of visible light owing to a longer wavelength allows a clear vision of haze. The SWIR light from nightglow facilitates night vision, including during dark moons. Hence, SWIR photodetection has been extensively utilized in various applications such as medical diagnostics [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], semiconductor inspection [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], astronomy [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], face recognition [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], and automotive [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Furthermore, broadband photodetection, which senses both visible and SWIR lights, is critical for compensating SWIR imaging. In automotives, for example, it is beneficial to render a color on SWIR imaging to identify traffic lights or road conditions [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eTo date, commercially available InGaAs photodiodes epitaxially grown on InP substrates have been predominantly employed for SWIR photodetection. However, the high material costs and limited responsivities of InGaAs photodiodes without carrier multiplications restrict their widespread usage in consumer products. Hence, various emerging materials such as graphene [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], quantum dots (QDs) [\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], and black phosphorus [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] have been proposed for implementing highly responsive SWIR photodetectors in diverse device structures such as PN diodes [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], Schottky junction diodes [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], and field effect transistors (FETs) [\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Furthermore, broadband photodetection has been demonstrated by adjoining a material with another material of a larger bandgap [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. However, previous studies have relied on unintentionally present charge traps to obtain a photocurrent gain. A strong confinement of photogenerated carriers in the traps may result in a high responsivity; however, a slow response time is imminent owing to the uncontrollable delayed release of trapped charges. Ni et al. reported an ultrahigh responsivity of 10\u003csup\u003e9\u003c/sup\u003e A/W at a wavelength of 1450 nm in a Si QDs/graphene FET; however, its slow response time of 3.4 s is unfavorable for the aforementioned applications [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Achieving high responsivities and fast responses in photodetectors remains challenging.\u003c/p\u003e\u003cp\u003eHerein, we present a high-performance broadband photodetector exhibiting fast photocarrier multiplication by embedding a potential trap formed by a Ge homojunction and a mixed-dimensional van der Waals (vdW) heterojunction (MoS\u003csub\u003e2\u003c/sub\u003e/Ge). The vdW heterojunctions of two-dimensional (2D) transition metal dichalcogenides (TMDCs) on conventional group IV or III\u0026ndash;V semiconductors introduce more degrees of freedom to heterostructure band engineering because TMDCs can easily form heterojunctions via vdW forces regardless of the lattice constants [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. The significant bandgap energy differences between TMDCs and semiconductor materials allow for creative band engineering to achieve broadband photodetectors [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], unlike previous attempts using bulk III\u0026ndash;V heterojunctions. Moreover, double junctions consisting of vdW heterojunctions and homojunctions construct an engineered potential trap. While a prolonged stay of captured photocarriers in unintentionally present defect/interface trap results in an extremely slow response, the photocarriers in the engineered potential trap are instantly recombined upon removal of illumination, providing a high responsivity and a fast response time, simultaneously.\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eDevice scheme\u003c/h2\u003e\u003cp\u003eIn this study, we employed a MoS\u003csub\u003e2\u003c/sub\u003e/Ge vdW heterojunction a Ge homojunction to achieve broadband and ultrafast photodetection. The vdW heterojunction between MoS\u003csub\u003e2\u003c/sub\u003e and Ge exhibited broadband photodetection owing to a significant bandgap energy difference (Eg_MoS\u003csub\u003e2\u003c/sub\u003e: 1.4\u0026ndash;2.2 eV [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]; Eg_Ge: 0.66 eV [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]). Moreover, in the n-Ge/p-Ge/MoS\u003csub\u003e2\u003c/sub\u003e double junction heterostructure, holes can be confined in the p-Ge region by tailoring the valence band. The accumulated photogenerated holes in the p-Ge lower the electron barrier between p-Ge and MoS\u003csub\u003e2\u003c/sub\u003e, resulting in a photocurrent gain and a high responsivity [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. The engineered hole confinement, in contrast to unintentional charge traps, exhibits a rapid diminishment of trapped holes upon the removal of light, thereby maintaining a fast response time.\u003c/p\u003e\u003cp\u003eA schematic illustration of the MoS\u003csub\u003e2\u003c/sub\u003e/Ge double junction phototransistor is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea. The device is composed of a p-Ge/n-Ge homojunction and a p-Ge/n-MoS\u003csub\u003e2\u003c/sub\u003e heterojunction. The p-Ge shared by the two junctions is a base that serves as a hole confinement region. The n-MoS\u003csub\u003e2\u003c/sub\u003e and n-Ge functioned as an emitter and collector, respectively. A 100-nm-thick p-Ge was achieved via B-ion implantation on an n-Ge substrate, followed by fine etching in a dilute solution comprising NH\u003csub\u003e4\u003c/sub\u003eOH and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e in Supporting Information). Prior to the transfer of the MoS\u003csub\u003e2\u003c/sub\u003e flake, the active area was defined by a circular opening with a diameter of 20 \u0026micro;m in an Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e layer.\u003c/p\u003e\u003cp\u003eThe details of the double junction phototransistor fabrication process and the optical image of the fabricated device are shown in Figure S2 (Supporting Information). The thickness of the transferred MoS\u003csub\u003e2\u003c/sub\u003e flakes was measured to be approximately 6.6 nm using atomic force microscopy (AFM), as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb. The AFM image shows that the MoS\u003csub\u003e2\u003c/sub\u003e flakes uniformly coated the exposed p-Ge region. Raman spectroscopic measurements were performed on the MoS\u003csub\u003e2\u003c/sub\u003e/Ge vdW heterojunction. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec, three Raman peaks appeared at 300.8, 383.8, and 408.8 cm\u003csup\u003e-1\u003c/sup\u003e, which corresponded to the Ge\u0026ndash;Ge phonon mode in Ge [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], as well as the E12g and A1g phonon modes in MoS\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], respectively. These results indicate the pristine quality of MoS\u003csub\u003e2\u003c/sub\u003e in the junction region after transfer. The interface of MoS\u003csub\u003e2\u003c/sub\u003e and Ge was characterized by a transmission electron microscopy (TEM) as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed. A stack of multilayer MoS\u003csub\u003e2\u003c/sub\u003e was intact on the Ge, forming the heterojunction. Despite immediate transfer of MoS\u003csub\u003e2\u003c/sub\u003e after cleaning the Ge surface, a formation of a native oxide could not be avoided. Nonetheless, the very thin thickness of the native oxide, less than 2 nm, hardly affects carrier transport.\u003c/p\u003e\u003cp\u003eThe energy band diagram of Ge/MoS\u003csub\u003e2\u003c/sub\u003e double junction phototransistor was experimentally determined (see Fig. S3 and text in Supporting Information). To determine workfunctions the surface potentials of p-Ge, MoS\u003csub\u003e2\u003c/sub\u003e, and the p-Ge/MoS\u003csub\u003e2\u003c/sub\u003e junction were 0.47, 0.19, and 0.2 eV, respectively, as measured using kelvin probe force microscopy (KPFM). The indiscernible potential difference between MoS\u003csub\u003e2\u003c/sub\u003e and p-Ge/MoS\u003csub\u003e2\u003c/sub\u003e could be attributable to the relatively thick MoS2 (6 nm) in which the Ge underneath has little effect on the MoS\u003csub\u003e2\u003c/sub\u003e top surface. The bandgap energy of Ge was estimated using the Tauc plot to be 0.66 eV, which agrees with the value determined using electron energy loss spectroscopy (EELS) [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The bandgap energy of MoS\u003csub\u003e2\u003c/sub\u003e and electron affinities were derived from references [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. At equilibrium, the energy band diagram of the MoS\u003csub\u003e2\u003c/sub\u003e/p-Ge/n-Ge heterojunction reveals a staggered-gap (type II) at MoS\u003csub\u003e2\u003c/sub\u003e/p-Ge. A conduction band offset and a valence band offset of 0.6 eV and 1.44 eV, respectively, were estimated.\u003c/p\u003e\u003cp\u003eThe carrier transport and amplification mechanism in the device can be understood in terms of the resulting energy band diagram, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee. The significant bandgap difference between Ge and MoS\u003csub\u003e2\u003c/sub\u003e contributed primarily to a high energy barrier to holes in the p-Ge instead of a conduction band offset in the heterojunction. Such dissimilar energy barriers in the heterojunction enabled MoS\u003csub\u003e2\u003c/sub\u003e to function as an ideal emitter, where more electrons from MoS\u003csub\u003e2\u003c/sub\u003e were transferred to p-Ge than holes from p-Ge to MoS\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. The hole current injected via the p-Ge considered as a base would not propagate to MoS\u003csub\u003e2\u003c/sub\u003e (emitter); as such, electrons were induced from the emitter efficiently. The induced electrons were transported over the base and collected by the n-Ge, which is known as a collector. When the device functions as a photodetector, a positive bias is applied to the n-Ge with respect to the emitter (MoS\u003csub\u003e2\u003c/sub\u003e), while the base (p-Ge) remains open. Hence, the base\u0026ndash;emitter (p-Ge/n-MoS\u003csub\u003e2\u003c/sub\u003e) is forward biased, whereas the base\u0026ndash;collector (p-Ge/n-Ge) is reverse-biased. The potential of the base should be determined by equalizing the current across each heterojunction; therefore, the bias is primarily allocated to the reverse bias of the base\u0026ndash;collector junction, as denoted by the black lines in the figure. When light is incident on n-MoS\u003csub\u003e2\u003c/sub\u003e, visible light is primarily absorbed in the MoS\u003csub\u003e2\u003c/sub\u003e region, and SWIR light transparent to the MoS\u003csub\u003e2\u003c/sub\u003e is absorbed by Ge. Electrons and holes are photogenerated across the emitter\u0026ndash;base heterojunction transport to the emitter and base, respectively. The electrons in the emitter flows out to the contact, but the holes are confined in the base. Hence, the accumulation of holes in the base lowers the energy barriers, particularly in the emitter\u0026ndash;base heterojunction, thereby resulting in an injection of electrons from the emitter to the base, followed by a drift of electrons to the collector. As such, one photogenerated hole can induce more than one electron, enabling a high responsivity exceeding 100% external quantum efficiency (EQE).\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eElectrical characterization\u003c/h3\u003e\n\u003cp\u003eElectrical measurements were performed on an n-MoS\u003csub\u003e2\u003c/sub\u003e/p-Ge/n-Ge double junction phototransistor under dark conditions at room temperature. First, the p-Ge (base, B)/n-MoS\u003csub\u003e2\u003c/sub\u003e (emitter, E) heterojunction and p-Ge (B)/n-Ge (collector, C) homojunctions were separately characterized. Under a voltage swept from \u0026minus;\u0026thinsp;4 to 4 V, current rectifying behaviors were clearly observed at both p\u0026ndash;n junctions, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea. The ON/OFF current ratios (I\u003csub\u003eON\u003c/sub\u003e/I\u003csub\u003eOFF\u003c/sub\u003e) of the B\u0026ndash;E and B\u0026ndash;C junctions were approximately 2.9\u0026times;10\u003csup\u003e7\u003c/sup\u003e and 1.5\u0026times;10\u003csup\u003e3\u003c/sup\u003e, respectively. Saturation current in p-Ge/n-Ge homojunction was much higher than that in p-Ge/n-MoS\u003csub\u003e2\u003c/sub\u003e heterojunction because of germanium\u0026rsquo;s narrow bandgap and a larger junction area of B-E junction (314 \u0026micro;m\u003csup\u003e2\u003c/sup\u003e) compared to that of B-C junction (11,309 \u0026micro;m\u003csup\u003e2\u003c/sup\u003e). The ideality factor (\u003cem\u003en\u003c/em\u003e) was estimated from the plot of ln(\u003cem\u003eI\u003c/em\u003e) vs. \u003cem\u003eV\u003c/em\u003e, and the values were 1.21 and 1.05 for the p-Ge/n-MoS\u003csub\u003e2\u003c/sub\u003e heterojunction and p-Ge/n-Ge junction, respectively. The slight deviations from the ideal diode can be ascribed to interface defects at the junction or additional series resistance [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb shows the input characteristics (\u003cem\u003eI\u003c/em\u003e\u003csub\u003eB\u003c/sub\u003e\u0026ndash;\u003cem\u003eV\u003c/em\u003e\u003csub\u003eBE\u003c/sub\u003e, where \u003cem\u003eI\u003c/em\u003e\u003csub\u003eB\u003c/sub\u003e and \u003cem\u003eV\u003c/em\u003e\u003csub\u003eBE\u003c/sub\u003e are the base current and base\u0026ndash;emitter voltage, respectively) of the device with different \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCB\u003c/sub\u003e biases. As observed in a forward-biased p\u0026ndash;n junction, \u003cem\u003eI\u003c/em\u003e\u003csub\u003eB\u003c/sub\u003e increased exponentially with \u003cem\u003eV\u003c/em\u003e\u003csub\u003eBE\u003c/sub\u003e. As \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCB\u003c/sub\u003e increased, \u003cem\u003eI\u003c/em\u003e\u003csub\u003eB\u003c/sub\u003e decreased and then rapidly saturated, implying that \u003cem\u003eI\u003c/em\u003e\u003csub\u003eB\u003c/sub\u003e is independent of the band shape above \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCB\u003c/sub\u003e = 0.15 V because the reverse current of the base\u0026ndash;collector junction had saturated. The output characteristics (\u003cem\u003eI\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e\u0026ndash;\u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e, where \u003cem\u003eI\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e and \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e are the collector current and collector\u0026ndash;emitter voltage, respectively) in the common-emitter mode were measured at \u003cem\u003eI\u003c/em\u003e\u003csub\u003eB\u003c/sub\u003e at steps of 200 nA, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec. It was observed that the input base current amplified under a \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e of \u0026gt;\u0026thinsp;~\u0026thinsp;3.5 V. At low \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e values, it was insufficient to tunnel the native oxide of Ge and lower the potential barrier on the B\u0026ndash;E junction owing to the difference in resistance between the B\u0026ndash;E and B\u0026ndash;C junctions. Hence, \u003cem\u003eI\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e increased exponentially after a sufficient \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e was applied. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed shows the combined plot of \u003cem\u003eI\u003c/em\u003e\u003csub\u003eB\u003c/sub\u003e and \u003cem\u003eI\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e vs. \u003cem\u003eV\u003c/em\u003e\u003csub\u003eBE\u003c/sub\u003e, which is known as the Gummel plot. The common-emitter current gain (\u003cem\u003eβ\u003c/em\u003e), defined as \u003cem\u003eI\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e/\u003cem\u003eI\u003c/em\u003e\u003csub\u003eB\u003c/sub\u003e, is shown on the right axis in the figure. As \u003cem\u003eV\u003c/em\u003e\u003csub\u003eBE\u003c/sub\u003e increased, both \u003cem\u003eI\u003c/em\u003e\u003csub\u003eB\u003c/sub\u003e and \u003cem\u003eI\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e increased exponentially in general. The \u003cem\u003eβ\u003c/em\u003e at \u003cem\u003eV\u003c/em\u003e\u003csub\u003eBE\u003c/sub\u003e ˃ 1 V was distinct because the non-ideal recombination current at a low \u003cem\u003eV\u003c/em\u003e\u003csub\u003eBE\u003c/sub\u003e did not increase \u003cem\u003eI\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e. To the best of our knowledge, a maximum \u003cem\u003eβ\u003c/em\u003e value of approximately 29, which is the highest value recorded among 2D and three-dimensional (3D) vdW junction devices, has been reported. As \u003cem\u003eV\u003c/em\u003e\u003csub\u003eBE\u003c/sub\u003e increased further, the increase in \u003cem\u003eI\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e declined compared with that of \u003cem\u003eI\u003c/em\u003e\u003csub\u003eB\u003c/sub\u003e, and \u003cem\u003eβ\u003c/em\u003e diminished. This contributed to a high-level injection and series resistance, resulting in a simultaneous slope-over in both the \u003cem\u003eI\u003c/em\u003e\u003csub\u003eB\u003c/sub\u003e and \u003cem\u003eI\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e, as shown in the figure.\u003c/p\u003e\u003cp\u003eThe electrical performance of the device was compared with those of previously reported hot electron transistors and heterojunction bipolar transistors based on 2D materials in terms of \u003cem\u003eβ\u003c/em\u003e and the collector current density (\u003cem\u003eJ\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e). As shown in Figure S5, the n-MoS\u003csub\u003e2\u003c/sub\u003e/p-Ge/n-Ge double junction phototransistor exhibited the highest \u003cem\u003eJ\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e along with a decently high \u003cem\u003eβ\u003c/em\u003e. Devices such as photodetectors exploit these favorable performances, such as a high \u003cem\u003eβ\u003c/em\u003e to amplify photo-induced holes in the base region, which will be discussed below. Additionally, MoS\u003csub\u003e2\u003c/sub\u003e/Ge double junction devices can be potentially deployed as electrical devices (e.g., switches and amplifiers).\u003c/p\u003e\n\u003ch3\u003ePhotoresponse characteristics\u003c/h3\u003e\n\u003cp\u003eThe photoresponse of the n-MoS\u003csub\u003e2\u003c/sub\u003e/p-Ge/n-Ge double junction phototransistor was characterized by illuminating either a visible (466 nm) or SWIR (1550 nm) laser at room temperature. A positive \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e was applied to the device with an open base, while maintaining the n-MoS\u003csub\u003e2\u003c/sub\u003e (E)/p-Ge (B) junction in forward bias and the p-Ge (B)/n-Ge (C) junction in reverse bias. Because the base is opened, the base current is governed by thermal generation in the dark and photogeneration in light. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea shows the \u003cem\u003eI\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e\u0026ndash;\u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e curves under 466 and 1550 nm illumination under the same optical irradiance of 10 mW/cm\u003csup\u003e2\u003c/sup\u003e on a linear scale, and the inset shows the \u003cem\u003eI\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e\u0026ndash;\u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e curves on a semi-logarithmic scale. An increase in \u003cem\u003eI\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e was observed for both the 466 and 1550 nm illuminations. Despite the lower photon energy of the 1550 nm light, which implies a higher number of incident photons at the same irradiance, the photoresponse of the 466 nm light was greater than that of the 1550 nm light. Because of the long penetration depth of 20 \u0026micro;m for the 1550 nm light in Ge [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e], all the lights at 1550 nm were not absorbed in the p-Ge, whereas incident light was partially absorbed at the p-Ge/n-Ge junction.\u003c/p\u003e\u003cp\u003eSubsequently, the time-resolved photocurrent (\u003cem\u003eI\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e) was characterized based on optical incident powers of 1, 3, 10, 30, 100, 300 and 1000 mW/cm\u003csup\u003e2\u003c/sup\u003e (Figure S6 in Supporting Information). The light modulated at a frequency of 1 kHz was illuminated on the device with a \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e of 4 V. When the incident light power increased, the photocurrent increased linearly with a slope of 1.01 and 0.93 under 466 and 1550 nm illuminations, respectively, as shown in Figure S6b and d. For a more quantitative analysis of the response time, the transient photocurrent responses of the 466 and 1550 nm light were normalized, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb. The response time (\u003cem\u003et\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e) is defined as \u003cem\u003et\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e = (\u003cem\u003et\u003c/em\u003e\u003csub\u003erise\u003c/sub\u003e + \u003cem\u003et\u003c/em\u003e\u003csub\u003efall\u003c/sub\u003e) /2, where \u003cem\u003et\u003c/em\u003e\u003csub\u003erise\u003c/sub\u003e is the rising time when the light is \u0026ldquo;on,\u0026rdquo; and \u003cem\u003et\u003c/em\u003e\u003csub\u003efall\u003c/sub\u003e is the falling time when the light is \u0026ldquo;off.\u0026rdquo; For 466 nm laser modulation, the \u003cem\u003et\u003c/em\u003e\u003csub\u003erise\u003c/sub\u003e and \u003cem\u003et\u003c/em\u003e\u003csub\u003efall\u003c/sub\u003e were estimated to be 202.3 \u0026micro;s and 88.1 \u0026micro;s, respectively, giving rise to the tr of 145 \u0026micro;s. Under the illumination of the 1550 nm laser, a tr of 224 \u0026micro;s was obtained based on \u003cem\u003et\u003c/em\u003e\u003csub\u003erise\u003c/sub\u003e and \u003cem\u003et\u003c/em\u003e\u003csub\u003efall\u003c/sub\u003e of 214.9 and 232.8 \u0026micro;s, respectively. The extracted response times were limited by the maximum sampling rate of 110 \u0026micro;s, and the actual response speed was expected to be higher.\u003c/p\u003e\u003cp\u003eThe specific detectivity (\u003cem\u003eD\u003c/em\u003e*) is defined as \u003cem\u003eD\u003c/em\u003e* = \u003cem\u003eR\u003c/em\u003e \u0026times; (\u003cem\u003eA\u003c/em\u003e\u0026middot;\u003cem\u003eBW\u003c/em\u003e)\u003csup\u003e1/2\u003c/sup\u003e/\u003cem\u003ei\u003c/em\u003e\u003csub\u003en\u003c/sub\u003e, where \u003cem\u003eR\u003c/em\u003e is the responsivity, \u003cem\u003eA\u003c/em\u003e is the area, \u003cem\u003eBW\u003c/em\u003e is the bandwidth, and \u003cem\u003ei\u003c/em\u003e\u003csub\u003en\u003c/sub\u003e is the measured noise current. \u003cem\u003eD\u003c/em\u003e* can be estimated by assuming that the shot noise is dominant. The shot noise can be expressed as \u003cem\u003ei\u003c/em\u003e\u003csub\u003en\u003c/sub\u003e = (2\u0026middot;\u003cem\u003ee\u003c/em\u003e\u0026middot;\u003cem\u003eI\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e\u0026middot;\u003cem\u003eBW\u003c/em\u003e)\u003csup\u003e1/2\u003c/sup\u003e, where \u003cem\u003ee\u003c/em\u003e is the electron charge, and \u003cem\u003eI\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e is the dark current. However, non-Ohmic contacts on the 2D materials and fluctuation of carrier transport over the vdW heterojunction may result in dominant noise components. For an accurate estimation of \u003cem\u003eD\u003c/em\u003e*, the noise power spectral density (NPSD) of the dark current was measured at various \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e values, as shown in Figure S7 (Supporting Information). The NPSD curves for all biases indicated a 1/f dependence. A considerable increase in the spectral noise density as \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e increased was observed. A frequency of 60 Hz and its harmonics were not the intrinsic noise of the device; instead, they originated from the 60 Hz power line. The noise currents with a \u003cem\u003eBW\u003c/em\u003e of 1 kHz when \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e were 1 and 4 V were 1.01\u0026times;10\u003csup\u003e\u0026ndash;11\u003c/sup\u003e and 9.92\u0026times;10\u003csup\u003e\u0026ndash;10\u003c/sup\u003e A/Hz\u003csup\u003e0.5\u003c/sup\u003e, respectively. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec and d show the responsivity, EQE, and resulting \u003cem\u003eD\u003c/em\u003e* vs. \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e for visible and SWIR lights, respectively (see calculation details in the Methods section). As \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e increased, \u003cem\u003eR\u003c/em\u003e and EQE increased linearly and reached maximum values of 7.6 A/W and 2,024%, respectively, for the 466 nm laser. Meanwhile, under the 1550 nm laser illumination, \u003cem\u003eR\u003c/em\u003e and EQE increased at \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e \u0026gt;0.5 V owing to the potential barrier of the B\u0026ndash;E junction and the absence of photogenerated carriers in MoS\u003csub\u003e2\u003c/sub\u003e, reaching maximum values of 4.7 A/W and 376%, respectively. Despite the increase in responsivity at higher \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e values at all detection ranges, the detectivity remained relatively constant because the noise current increased simultaneously. The maximum detectivities were 1.85\u0026times;10\u003csup\u003e8\u003c/sup\u003e and 8.01\u0026times;10\u003csup\u003e7\u003c/sup\u003e Jones under the 466 and 1550 nm illuminations, respectively. The detectivity was calculated by removing the input power noise (observed at intervals of 60 Hz, as shown in Figure S7). The detectivity was relatively low due to the high noise current caused by the high dark current. Additionally, Figure S8 shows the spectral responsivity and external quantum efficiency of the Ge/MoS\u003csub\u003e2\u003c/sub\u003e double junction phototransistor, confirming its broadband detection capability from visible to SWIR wavelengths via photocurrent amplification.\u003c/p\u003e\u003cp\u003ePhotocurrent multiplication in the n-MoS\u003csub\u003e2\u003c/sub\u003e/p-Ge/n-Ge double junction phototransistor was directly evidenced by a comparison with the photoresponses of the p-Ge/n-MoS\u003csub\u003e2\u003c/sub\u003e heterojunction and p-Ge/n-Ge homojunction under 466 and 1550 nm illumination (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee and f). Under the 466 nm illumination, the photocurrents (EQE) when the bias voltage was 4 V were 2.96\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;7\u003c/sup\u003e A (69.7%) and 1.54\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;7\u003c/sup\u003e A (36.2%) in the p-Ge/n-Ge homojunction and p-Ge/n-MoS\u003csub\u003e2\u003c/sub\u003e heterojunction, respectively, which indicate EQE values of less 100% (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee). Meanwhile, the photocurrent (EQE) in the double junction phototransistor was 8.15\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e A (1,918.8%) at \u003cem\u003eV\u003c/em\u003e\u003csub\u003eCE\u003c/sub\u003e = 4 V, which implies that the photoresponse gain was present. The photocurrent gain (\u003cem\u003eβ\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e) of the double junction phototransistor, as calculated for 466 and 1550 nm illuminations, is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg. At higher bias voltages, \u003cem\u003eβ\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e reached the maximum measured values, i.e., 29.1 and 11.6 for 466 and 1550 nm, respectively, and these values were similar to the base current gain obtained in the aforementioned electrical characterization.\u003c/p\u003e\u003cp\u003eFor photodetectors and image sensors, responsivity and response speed are critical figures-of-merit. To detect weak light in an image sensor, the photodetector must have both a fast response time and a high responsivity. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the cut-off frequencies and responsivities of several previously reported broadband photodetectors. Without photocurrent gain, devices exhibit a rapid response time because carriers are photogenerated and then promptly vanish in response to the on/off of light [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. On the other hand, in the devices with a high responsivity due to photocurrent gain, photogenerated carriers do not completely disappear when the light is switched off, resulting in a long response time [\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. In other words, it has been challenging to develop desirable features in both. It is worth noting that our phototransistor outperformed other photodetectors in terms of response time and responsivity. This capability is credited with broadband imaging, including SWIR for night vision and harsh environments in self-driving.\u003c/p\u003e\u003cp\u003eAdditionally, the broadband imaging capability of our device was investigated. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea shows a schematic diagram of the measurement systems used for broadband imaging. A smile image, which was mounted onto the XY-axis motorized stage, was placed between the light source and lens. The light incident from the 466 and 1550 nm lasers was focused onto the phototransistor via the lens after it passed through the object. Visible/SWIR smile images of 32 \u0026times; 32 pixels are clearly depicted in Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb\u0026ndash;c. These results imply that the device proposed herein can be utilized as a broadband imaging sensor from the visible to SWIR light range.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn this study, we demonstrate a MoS\u003csub\u003e2\u003c/sub\u003e/Ge double junction phototransistor and investigated its electrical and photoresponse characteristics. The electrical properties obtained demonstrated their potential as an electronic device and a photodetector with β\u0026thinsp;=\u0026thinsp;29. The MoS\u003csub\u003e2\u003c/sub\u003e/Ge phototransistor allowed broadband detection from the visible to SWIR wavelength range. The double junction phototransistor exhibited high photocurrent amplification, with \u003cem\u003eβ\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;29.1 (11.6) at 466 (1550) nm. Moreover, the fabricated phototransistor exhibited a high responsivity of 7.4 (4.7) A/W and fast \u003cem\u003et\u003c/em\u003e\u003csub\u003erise\u003c/sub\u003e (\u003cem\u003et\u003c/em\u003e\u003csub\u003efall\u003c/sub\u003e) of 202.3 (214.9) and 88.1 (232.8) \u0026micro;s, respectively, under a 466 (1550) nm illumination. The fast broadband photodetection demonstrated in this study, which was achieved by utilizing a heterogeneously integrated Ge/TMDC structure, will greatly facilitate bringing improved photodetectors to the market, such as an eye safe detector operating in the 1550 nm wavelength as opposed to the harmful 940 nm wavelength, or sensors that allow to obtain clear visibility in adverse weather conditions. The concept of a vdW Ge/TMDC heterojunction addition to conventional homojunction device can be adopted to improve the performance of many conventional III\u0026ndash;V devices that operate with inferior fundamental operations that limit their performances with much cheaper cost. The 2D/3D heterostructure concept demonstrated here removes this bottleneck, thereby providing opportunities for the development of ultrahigh-performance electric and optoelectronic devices.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eMaterial characterization\u003c/h2\u003e\u003cp\u003eMorphology was measured using AFM (XE100, Park Systems) in non-contact mode. Kelvin probe force microscopy measurement was performed using AFM (XN-10, Park Systems) in non-contact mode. Micro-Raman spectroscopy measurements (LabRam HR Evolution, Horiba) of the Ge/MoS\u003csub\u003e2\u003c/sub\u003e double junction phototransistor were performed based on a spatial resolution of 1 \u0026micro;m and a 532 nm excitation laser under ambient conditions. The sample for TEM analysis was prepared using a focused ion beam system (Quanta 3D FEG, FEI). TEM was performed using a high-resolution TEM (JEM-2100F, JEOL) with an operating voltage of 200 kV.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eElectrical and optoelectrical measurements\u003c/h3\u003e\n\u003cp\u003eElectrical and optoelectrical characteristic measurements were performed using a semiconductor parameter analyzer (4200A-SCS, Keithley Instruments) with 466 and 1550 nm diode pumped solid-state lasers (Civil laser). The transient characteristics were measured using a source meter (2614 B, Keithley Instruments) with pulsed 466 and 1550 nm lasers. The spectral responsivities were measured using monochomater (MonoRa200, Dongwoo Optron) with Xenon lamp. The NPSDs were measured at a sampling rate of 1,600 Hz under dark conditions using a dynamic signal analyzer (35670A, Agilent).\u003c/p\u003e\n\u003ch3\u003eResponse speed, responsivity, detectivity, and photocurrent gain extraction\u003c/h3\u003e\n\u003cp\u003eThe \u003cem\u003et\u003c/em\u003e\u003csub\u003erise\u003c/sub\u003e and \u003cem\u003et\u003c/em\u003e\u003csub\u003efall\u003c/sub\u003e were defined as the time intervals that increased from 10\u0026ndash;90% at the peak values and decreased from 90\u0026ndash;10%, respectively.\u003c/p\u003e\u003cp\u003eTo extract the responsivity, the photocurrent was calculated as \u003cem\u003eI\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e = \u003cem\u003eI\u003c/em\u003e\u003csub\u003elight\u003c/sub\u003e - \u003cem\u003eI\u003c/em\u003e\u003csub\u003edark\u003c/sub\u003e, where \u003cem\u003eI\u003c/em\u003e\u003csub\u003elight\u003c/sub\u003e is the measured current with illuminations of various power intensities and wavelengths, and \u003cem\u003eI\u003c/em\u003e\u003csub\u003edark\u003c/sub\u003e is the measured current under dark conditions. The responsivity was calculated as \u003cem\u003eR\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eI\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e/\u003cem\u003eP\u003c/em\u003e\u003csub\u003ein\u003c/sub\u003e, where \u003cem\u003eI\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e and \u003cem\u003eP\u003c/em\u003e\u003csub\u003ein\u003c/sub\u003e are the photocurrent and incident optical power, respectively.\u003c/p\u003e\u003cp\u003eTo characterize in, the measured current NPSD was square-rooted and integrated by the \u003cem\u003eBW\u003c/em\u003e, where \u003cem\u003eBW\u003c/em\u003e is the specified bandwidth. The noise equivalent power (NEP) of our device was calculated as NEP\u0026thinsp;=\u0026thinsp;\u003cem\u003ei\u003c/em\u003e\u003csub\u003en\u003c/sub\u003e/\u003cem\u003eR\u003c/em\u003e, where in is the total noise current in units of A\u0026middot;Hz\u003csup\u003e-0.5\u003c/sup\u003e. The detectivity is expressed as \u003cem\u003eD\u003c/em\u003e* = \u003cem\u003eA\u003c/em\u003e\u003csup\u003e-0.5\u003c/sup\u003e/NEP, where \u003cem\u003eA\u003c/em\u003e is the area of the heterojunction phototransistor.\u003c/p\u003e\u003cp\u003eThe photocurrent gain was extracted as \u003cem\u003eβ\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eI\u003c/em\u003e\u003csub\u003eph,tr\u003c/sub\u003e/\u003cem\u003eI\u003c/em\u003e\u003csub\u003eph,pn\u003c/sub\u003e, where \u003cem\u003eI\u003c/em\u003e\u003csub\u003eph,tr\u003c/sub\u003e is the photocurrent of the vdW Ge/MoS\u003csub\u003e2\u003c/sub\u003e heterojunction phototransistor, and \u003cem\u003eI\u003c/em\u003e\u003csub\u003eph,pn\u003c/sub\u003e is the photocurrent of the p\u0026ndash;n junctions.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eASSOCIATED CONTENT\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupporting Information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eInclude details about the fabrication process, characterization of the energy band diagram, comparison of electrical performance, and additional optoelectronic characteristics (PDF) \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAUTHOR INFORMATION\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorresponding Author\u003c/p\u003e\n\u003cp\u003e*Junseok Heo -\u0026nbsp;Department\u0026nbsp;of Electrical and Computer Engineering, Ajou University, Suwon 16499, South Korea; Email: [email protected]\u003c/p\u003e\n\u003cp\u003eAuthor Contributions\u003c/p\u003e\n\u003cp\u003eY.P. fabricated the devices and performed the electrical and optical measurements. H.B.J and H.Y.J performed the material characterizations. Y.P., S.S., and J.H. analyzed the experiments and wrote the manuscript. All authors contributed to the discussion and analysis of the results of the manuscript. J.H. supervised the project.\u003c/p\u003e\n\u003cp\u003eNotes\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFUNDING\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was supported by the National R\u0026amp;D Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (RS-2024-00438811, RS-2025-00564261, RS-2025-02217113).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analysed during the current study available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eNaboulsi, M. A. Fog attenuation prediction for optical and infrared waves. \u003cem\u003eOpt. Eng.\u003c/em\u003e \u003cb\u003e43\u003c/b\u003e (2), 319. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1117/1.1637611\u003c/span\u003e\u003cspan address=\"10.1117/1.1637611\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2004).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDriggers, R. G., Hodgkin, V. \u0026amp; Vollmerhausen, R. What good is SWIR? Passive day comparison of VIS, NIR, and SWIR. \u003cem\u003eInfrared Imaging Syst. Des. Anal. Model. Test. XXIV\u003c/em\u003e. \u003cb\u003e8706\u003c/b\u003e, 87060L. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1117/12.2016467\u003c/span\u003e\u003cspan address=\"10.1117/12.2016467\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2013).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMartin, T., Brubaker, R., Dixon, P., Gagliardi, M. A. \u0026amp; Sudol, T. 640x512 InGaAs focal plane array camera for visible and SWIR imaging, in \u003cem\u003eInfrared Technology and Applications XXXI\u003c/em\u003e, May vol. 5783, p. 12, (2005). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1117/12.603406\u003c/span\u003e\u003cspan address=\"10.1117/12.603406\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMalchow, D., Battaglia, J., Brubaker, R. \u0026amp; Ettenberg, M. High speed short wave infrared (SWIR) imaging and range gating cameras, in \u003cem\u003eThermosense XXIX\u003c/em\u003e, Apr. vol. 6541, p. 654106, (2007). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1117/12.721747\u003c/span\u003e\u003cspan address=\"10.1117/12.721747\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBernini, N., Bertozzi, M., Cerri, P. \u0026amp; Fedriga, R. I. SWIR Cameras for the Automotive Field: Two Test Cases, \u003cem\u003eISRN Automot. Eng.\u003c/em\u003e, vol. pp. 1\u0026ndash;11, Apr. 2014, (2014). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1155/2014/858979\u003c/span\u003e\u003cspan address=\"10.1155/2014/858979\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTsuboi, S. \u0026amp; Jin, T. Shortwave-infrared (SWIR) fluorescence molecular imaging using indocyanine green-antibody conjugates for the optical diagnostics of cancerous tumours, \u003cem\u003eRSC Adv.\u003c/em\u003e, vol. 10, no. 47, pp. 28171\u0026ndash;28179, Jul. (2020). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1039/d0ra04710d\u003c/span\u003e\u003cspan address=\"10.1039/d0ra04710d\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eQi, J. et al. Real-Time and High-Resolution Bioimaging with Bright Aggregation-Induced Emission Dots in Short-Wave Infrared Region, \u003cem\u003eAdv. Mater.\u003c/em\u003e, vol. 30, no. 12, Mar. (2018). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/adma.201706856\u003c/span\u003e\u003cspan address=\"10.1002/adma.201706856\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eYu, Z. et al. High-Resolution Shortwave Infrared Imaging of Vascular Disorders Using Gold Nanoclusters. \u003cem\u003eACS Nano\u003c/em\u003e. \u003cb\u003e14\u003c/b\u003e (4), 4973\u0026ndash;4981. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1021/acsnano.0c01174\u003c/span\u003e\u003cspan address=\"10.1021/acsnano.0c01174\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2020).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eNarang, N. \u0026amp; Bourlai, T. Face recognition in the SWIR band when using single sensor multi-wavelength imaging systems. \u003cem\u003eImage Vis. Comput.\u003c/em\u003e \u003cb\u003e33\u003c/b\u003e, 26\u0026ndash;43. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.imavis.2014.10.005\u003c/span\u003e\u003cspan address=\"10.1016/j.imavis.2014.10.005\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2015).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGoossens, S. et al. Broadband image sensor array based on graphene-CMOS integration. \u003cem\u003eNat. Photonics\u003c/em\u003e. \u003cb\u003e11\u003c/b\u003e (6), 366\u0026ndash;371. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1038/nphoton.2017.75\u003c/span\u003e\u003cspan address=\"10.1038/nphoton.2017.75\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2017).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eNi, Z. et al. Plasmonic Silicon Quantum Dots Enabled High-Sensitivity Ultrabroadband Photodetection of Graphene-Based Hybrid Phototransistors. \u003cem\u003eACS Nano\u003c/em\u003e. \u003cb\u003e11\u003c/b\u003e (10), 9854\u0026ndash;9862. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1021/acsnano.7b03569\u003c/span\u003e\u003cspan address=\"10.1021/acsnano.7b03569\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2017).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKufer, D. et al. Hybrid 2D-0D MoS2-PbS quantum dot photodetectors. \u003cem\u003eAdv. Mater.\u003c/em\u003e \u003cb\u003e27\u003c/b\u003e (1), 176\u0026ndash;180. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/adma.201402471\u003c/span\u003e\u003cspan address=\"10.1002/adma.201402471\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2015).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCao, R. et al. Black Phosphorous/Indium Selenide Photoconductive Detector for Visible and Near-Infrared Light with High Sensitivity. \u003cem\u003eAdv. Opt. Mater.\u003c/em\u003e \u003cb\u003e7\u003c/b\u003e (12), 1\u0026ndash;7. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/adom.201900020\u003c/span\u003e\u003cspan address=\"10.1002/adom.201900020\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2019).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eYe, L., Li, H., Chen, Z. \u0026amp; Xu, J. Near-Infrared Photodetector Based on MoS2/Black Phosphorus Heterojunction. \u003cem\u003eACS Photonics\u003c/em\u003e. \u003cb\u003e3\u003c/b\u003e (4), 692\u0026ndash;699. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1021/acsphotonics.6b00079\u003c/span\u003e\u003cspan address=\"10.1021/acsphotonics.6b00079\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2016).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGeum, D. M. et al. Arrayed MoS2\u0026ndash;In0.53Ga0.47As van der Waals Heterostructure for High-Speed and Broadband Detection from Visible to Shortwave-Infrared Light. \u003cem\u003eSmall\u003c/em\u003e \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/smll.202007357\u003c/span\u003e\u003cspan address=\"10.1002/smll.202007357\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2021).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHeves, E. \u0026amp; Gurbuz, Y. Highly Responsive, Solution-Based Al/PbS and Au-Ti/PbS Schottky Photodiodes for SWIR Detection, \u003cb\u003e14\u003c/b\u003e, 3, pp. 816\u0026ndash;820, (2014).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKim, S. G. et al. Infrared Detectable MoS2 Phototransistor and Its Application to Artificial Multilevel Optic-Neural Synapse. \u003cem\u003eACS Nano\u003c/em\u003e. \u003cb\u003e13\u003c/b\u003e (9), 10294\u0026ndash;10300. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1021/acsnano.9b03683\u003c/span\u003e\u003cspan address=\"10.1021/acsnano.9b03683\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2019).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHwang, A. et al. Visible and infrared dual-band imaging via Ge/MoS2van der Waals heterostructure. \u003cem\u003eSci. Adv.\u003c/em\u003e \u003cb\u003e7\u003c/b\u003e (51), 1\u0026ndash;9. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1126/sciadv.abj2521\u003c/span\u003e\u003cspan address=\"10.1126/sciadv.abj2521\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2021).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLee, C. H. et al. Design of p-WSe 2 /n‐Ge Heterojunctions for High‐Speed Broadband Photodetectors. \u003cem\u003eAdv. Funct. Mater.\u003c/em\u003e \u003cb\u003e2107992\u003c/b\u003e, 2107992. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/adfm.202107992\u003c/span\u003e\u003cspan address=\"10.1002/adfm.202107992\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2021).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChoi, W. et al. Recent development of two-dimensional transition metal dichalcogenides and their applications. \u003cem\u003eMater. Today\u003c/em\u003e. \u003cb\u003e20\u003c/b\u003e (3), 116\u0026ndash;130. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.mattod.2016.10.002\u003c/span\u003e\u003cspan address=\"10.1016/j.mattod.2016.10.002\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2017).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLopez-Sanchez, O. et al. Light generation and harvesting in a van der waals heterostructure. \u003cem\u003eACS Nano\u003c/em\u003e. \u003cb\u003e8\u003c/b\u003e (3), 3042\u0026ndash;3048. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1021/nn500480u\u003c/span\u003e\u003cspan address=\"10.1021/nn500480u\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2014).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePark, Y., Hwang, A. J., Lee, C., Yoo, G. \u0026amp; Heo, J. Broadband photodetection of MoS2/p-Ge/n-Ge bipolar heterojunction phototransistor, in \u003cem\u003eConference on Lasers and Electro-Optics, CLEO 2021 - Proceedings\u003c/em\u003e, 2021, p. STh5B.3, 2021, p. STh5B.3, (2021). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1364/cleo_si.2021.sth5b.3\u003c/span\u003e\u003cspan address=\"10.1364/cleo_si.2021.sth5b.3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZhao, Z. Y. \u0026amp; Liu, Q. L. Study of the layer-dependent properties of MoS2 nanosheets with different crystal structures by DFT calculations. \u003cem\u003eCatal. Sci. Technol.\u003c/em\u003e \u003cb\u003e8\u003c/b\u003e (7), 1867\u0026ndash;1879. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1039/c7cy02252b\u003c/span\u003e\u003cspan address=\"10.1039/c7cy02252b\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2018).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTrommer, J. et al. Enabling Energy Efficiency and Polarity Control in Germanium Nanowire Transistors by Individually Gated Nanojunctions. \u003cem\u003eACS Nano\u003c/em\u003e. \u003cb\u003e11\u003c/b\u003e (2), 1704\u0026ndash;1711. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1021/acsnano.6b07531\u003c/span\u003e\u003cspan address=\"10.1021/acsnano.6b07531\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2017).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSu, B. W. et al. A gate-tunable symmetric bipolar junction transistor fabricated: Via femtosecond laser processing, \u003cem\u003eNanoscale Adv.\u003c/em\u003e, vol. 2, no. 4, pp. 1733\u0026ndash;1740, Apr. (2020). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1039/d0na00201a\u003c/span\u003e\u003cspan address=\"10.1039/d0na00201a\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLi, H., Ye, L. \u0026amp; Xu, J. High-Performance Broadband Floating-Base Bipolar Phototransistor Based on WSe2/BP/MoS2 Heterostructure. \u003cem\u003eACS Photonics\u003c/em\u003e. \u003cb\u003e4\u003c/b\u003e (4), 823\u0026ndash;829. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1021/acsphotonics.6b00778\u003c/span\u003e\u003cspan address=\"10.1021/acsphotonics.6b00778\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2017).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePrucnal, S. et al. Superconductivity in single-crystalline aluminum- and gallium-hyperdoped germanium. \u003cem\u003ePhys. Rev. Mater.\u003c/em\u003e \u003cb\u003e3\u003c/b\u003e (5), 1\u0026ndash;10. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1103/PhysRevMaterials.3.054802\u003c/span\u003e\u003cspan address=\"10.1103/PhysRevMaterials.3.054802\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2019).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLee, C. et al. Anomalous lattice vibrations of single- and few-layer MoS2. \u003cem\u003eACS Nano\u003c/em\u003e. \u003cb\u003e4\u003c/b\u003e (5), 2695\u0026ndash;2700. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1021/nn1003937\u003c/span\u003e\u003cspan address=\"10.1021/nn1003937\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2010).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eNishimura, T., Luo, X., Matsumoto, S., Yajima, T. \u0026amp; Toriumi, A. Almost pinning-free bismuth/Ge and /Si interfaces. \u003cem\u003eAIP Adv.\u003c/em\u003e \u003cb\u003e9\u003c/b\u003e (9). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1063/1.5115535\u003c/span\u003e\u003cspan address=\"10.1063/1.5115535\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2019).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAnderson, B. \u0026amp; Anderson, R. \u003cem\u003eFundamentals of Semiconductor Devices\u003c/em\u003e. McGraw-Hill College; 1st edition, (2004).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChoudhary, N. et al. Two-dimensional lateral heterojunction through bandgap engineering of MoS2 via oxygen plasma. \u003cem\u003eJ. Phys. Condens. Matter\u003c/em\u003e. \u003cb\u003e28\u003c/b\u003e (36). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1088/0953-8984/28/36/364002\u003c/span\u003e\u003cspan address=\"10.1088/0953-8984/28/36/364002\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2016).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eYan, X. et al. High Performance Amplifier Element Realization via MoS2/GaTe Heterostructures. \u003cem\u003eAdv. Sci.\u003c/em\u003e \u003cb\u003e5\u003c/b\u003e (4), 1\u0026ndash;7. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/advs.201700830\u003c/span\u003e\u003cspan address=\"10.1002/advs.201700830\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2018).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eEng, P. C., Song, S. \u0026amp; Ping, B. State-of-the-art photodetectors for optoelectronic integration at telecommunication wavelength, \u003cem\u003eNanophotonics\u003c/em\u003e, vol. 4, no. 1. Walter de Gruyter GmbH, pp. 277\u0026ndash;302, Jan. (2015). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1515/nanoph-2015-0012\u003c/span\u003e\u003cspan address=\"10.1515/nanoph-2015-0012\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Photocurrent multiplication, potential trap, boradband photodetector, SWIR, van der Waals, germanium, MoS2","lastPublishedDoi":"10.21203/rs.3.rs-7341136/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7341136/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eBroadband photodetectors in the visible and short-wave infrared wavelengths have garnered significant interest in recent years as a desirable method to achieve better detection in adverse weather conditions. Many material combinations have been proposed to replace expensive III-V based photodetectors; however, the photodetection performance of these novel material and device concepts showed undesirable performances due to uncontrollable charge-trap-based photomultiplication, preventing fast photoresponse and gain. To solve this issue, we devised an engineered potential trap in Ge/MoS\u003csub\u003e2\u003c/sub\u003e double junction phototransistor which show a high responsivity of 7.6 A/W (corresponding to an external quantum efficiency of 2,024%) as well as a fast photoresponse of 88.1 \u0026micro;s. The maximum photocurrent gain reaches 29.1 with broadband imaging capability. This excellent performance is achieved through photogenerated hole confined in p-Ge clad by MoS\u003csub\u003e2\u003c/sub\u003e and n-Ge induced multiple electrons, which diminished rapidly via recombination upon removal of illumination. Our device concept enables creation of highly sensitive fast broadband imaging based on mixed dimensional van der Waals heterojunctions.\u003c/p\u003e","manuscriptTitle":"Fast Photo-carrier Multiplication by Engineered Potential Trap in MoS2/Ge Double Junction Phototransistor","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-01 08:45:50","doi":"10.21203/rs.3.rs-7341136/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-11-04T05:11:58+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-22T06:40:25+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-19T18:29:07+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"122717568126911334926457684708710630724","date":"2025-10-19T18:15:49+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-17T21:32:31+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"304790440628274200361914621392487669587","date":"2025-10-14T09:08:34+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"98306886118880076644061479871813481021","date":"2025-10-13T10:10:30+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"39083169198732912373539857795879229718","date":"2025-10-12T05:34:54+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-07T20:58:11+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"225252471934926154482795882976883413332","date":"2025-08-22T07:25:41+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-19T00:10:31+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-08-18T23:52:02+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-08-18T14:59:33+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-08-13T09:42:06+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-08-13T09:38:54+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a5b084d6-1003-41f5-9e09-85552b662651","owner":[],"postedDate":"September 1st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":53553010,"name":"Physical sciences/Engineering"},{"id":53553011,"name":"Physical sciences/Materials science"},{"id":53553012,"name":"Physical sciences/Nanoscience and technology"},{"id":53553013,"name":"Physical sciences/Optics and photonics"},{"id":53553014,"name":"Physical sciences/Physics"}],"tags":[],"updatedAt":"2026-01-12T16:06:21+00:00","versionOfRecord":{"articleIdentity":"rs-7341136","link":"https://doi.org/10.1038/s41598-026-35134-z","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2026-01-08 15:59:10","publishedOnDateReadable":"January 8th, 2026"},"versionCreatedAt":"2025-09-01 08:45:50","video":"","vorDoi":"10.1038/s41598-026-35134-z","vorDoiUrl":"https://doi.org/10.1038/s41598-026-35134-z","workflowStages":[]},"version":"v1","identity":"rs-7341136","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7341136","identity":"rs-7341136","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}