Opto-electrical decoupled phototransistor for starlight detection

Opto-electrical decoupled phototransistor for starlight detection | 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 Opto-electrical decoupled phototransistor for starlight detection Zhiyong Zhang, Shaoyuan Zhou, Xinyue Zhang, Ying Wang, dongyi Lin, and 8 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4705743/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Highly sensitive shortwave infrared (SWIR) detectors are essential for detecting weak radiation (typically below 10 − 8 W·Sr − 1 ·cm − 2 ·µm − 1 ) with high-end passive image sensors. However, mainstream SWIR detection technology is based on epitaxial photodiodes, which cannot effectively detect ultraweak infrared radiation due to the lack of inherent gain. Here, we developed a heterojunction-gated field-effect transistor (HGFET) consisting of a colloidal quantum dot (CQD)-based p-i-n heterojunction and a carbon nanotube (CNT) field-effect transistor, which achieves a high inherent gain based on an opto-electric decoupling mechanism for suppressing noise. The stacked heterojunction absorbs infrared radiation and separates electron-hole pairs. Then, the generated photovoltage tunes the drain current of the CNT FET through an Y 2 O 3 gate insulator. As a result, the HGFET significantly detects and amplifies SWIR signals with a high inherent gain while minimally amplifying noise, leading to a recorded specific detectivity above 10 14 Jones at 1300 nm and a recorded maximum gain-bandwidth product of 69.2 THz. Direct comparative testing indicated that the HGFET can detect weak infrared radiation at 0.46 nW/cm 2 levels; thus, compared to commercial and reported SWIR detectors, this detector is much more sensitive and enables starlight detection or vision. As the fabrication process is very compatible with CMOS readout integrated circuits, the HGFET is a promising SWIR detector for realizing passive night vision imaging sensors with high resolutions that are high-end, highly sensitive, and inexpensive. Physical sciences/Engineering/Electrical and electronic engineering Physical sciences/Nanoscience and technology/Nanoscale devices/Electronic devices infrared photodetector carbon nanotubes weak infrared radiation detection opto-electric decoupling sensitivity Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Extensive efforts have been dedicated to improving the detectivity and resolution of shortwave infrared (SWIR, within the band of 0.9–1.7 µm) photodetectors, which enable remote imaging, night vision, spectroscopy and object tracing 1–4 . Generally, the detection of weak infrared radiation (typically below 10 − 8 W·Sr − 1 ·cm − 2 ·µm − 1 ) places extremely high demands on the signal-to-noise ratio (SNR), also known as the detectivity of sensors; due to these demands, it is necessary to achieve high optical responses and low electrical noise 5 . Mainstream SWIR detectors rely on the diode configuration and are currently dominated by epitaxial semiconductors, such as indium gallium arsenide (InGaAs); through continuously improving material and interface quality, researchers have developed detectors with high specific detectivity (~ 10 13 Jones) based on an ultralow dark current below 1 nA/cm 2 and electrical noise approaching the technological limit 5–8 . The optical response of a diode detector is determined by the external quantum efficiency (EQE), which can reach as high as ~ 90% 5 ; thus, there is little room for improvement. Further improving the detectivity beyond 10 13 Jones, which enables the detection of weak infrared radiation at sub-1 nW/cm 2 levels (starlight) 9 , is challenging in a photodiode structure that lacks inherent gain and provides only one pair of carriers per single incident photon 5, 10 . Implementing an inherent gain mechanism is essential for enhancing the optical response, as exemplified in device architectures, such as avalanche photodiodes (APDs) and nanostructured field-effect transistors (FETs) 11–13 . Under a high electric field, photocarriers in APDs are accelerated and multiplied through impact ionization, achieving a high gain ( M ) that exceeds 10 5 when operating in Geiger mode for single-photon detection 14, 15 . However, due to the random ionization of charge carriers, APDs tend to exhibit significantly amplified excess noise 11, 16 . Emerging nanomaterials with facile solution processability and integration capability offer greater flexibility in infrared detector design, holding significant potential for constructing novel detectors with high gain and low costs 1, 2 . Recently, extensive infrared radiation detectors with nanostructured FET architectures have been reported to have inherent gains 17–21 . Quantum dot-sensitized graphene FET, a typical type of nanostructured phototransistor, achieved high photogain (up to 10 8 ) based on a trap-dominated photogating effect, but usually suffers from high dark current, noise levels, and limited response speed 9, 12 . More recently, researchers have also reported sensitized FETs based on large bandgap semiconductor channel materials with reduced dark current (0.1–100 nA) and high photogain 18, 22–24 . Almost all the reported FET detectors with high inherent gain have also been no substantial breakthrough in detectivity, since the noise and signal are simultaneously amplified in the same channel in charge of optical sensing and electrical amplification. Therefore, a SWIR detector with a well-designed device structure and operating mechanism is highly desired to achieve opto-electric decoupling, facilitating ultrahigh detectivity beyond 10 13 Jones and enabling passive starlight detection or vision. In this work, we present a heterojunction-gated field-effect transistor (HGFET) that achieves ultrahigh photogain and exceptionally low noise in the SWIR region, benefiting from a design that incorporates a comprehensive opto-electric decoupling mechanism. The stacked heterojunction absorbs infrared radiation and separates electron-hole pairs. Then, the generated photovoltage tunes the drain current of the CNT FET through an electrostatic gate coupling effect. As a result, optical sensing process and electrical amplification process are completely isolated in space. The opto-electric decoupling HGFET significantly detected and amplified SWIR signals with a high inherent gain of 1.5×10 6 while barely amplifying noise; in addition, the HGFET exhibited a recorded specific detectivity above 10 14 Jones at 1300 nm and a maximum gain-bandwidth product ( GBW ) of 15.5 GHz, enabling the detection of weak infrared radiation at 0.46 nW/cm 2 . The use of aligned CNTs in HGFETs further promoted the GBW to 69.2 THz, surpassing the theoretical limit of sensitized Si FETs and state-of-the-art InGaAs APDs 18, 25–27 . The results demonstrated that the HGFET is a promising SWIR detector for realizing high-end passive night vision image sensors with high resolution, high sensitivity, and low cost. HGFET structure Figure 1 a shows a schematic of the HGFET infrared detector, which consists of a CNT thin-film transistor gated by a PbS CQD/ZnO heterojunction (the detailed fabrication processes are provided in Methods and Supplementary Section 1). Local bottom-gated metal-oxide- semiconductor (MOS) FETs are fabricated on a randomly oriented semiconducting CNT film covered by an yttrium oxide (Y 2 O 3 ) film which acts as gate insulator to separate the photoelectric conversion component above and the electronic component below. A sputtered 40-nm layer of n-doped ZnO (with a dopant concentration of ~ 10 17 cm − 3 ) 28, 29 is deposited and patterned on a Y 2 O 3 /CNT film channel through photolithography and a lift-off process. A 150 nm-thick intrinsic PbS-halide CQD layer and a 30 nm-thick ethanedithiol (EDT)-treated p-doped PbS CQD layer (with a dopant concentration of 10 17 cm − 3 ) are spin-cast to form a p-i-n heterojunction, which generates a negative photovoltage through the absorption of infrared photons, the separation of photogenerated electron-hole pairs through the built-in field, and the accumulation of electrons at the ZnO/gate dielectric interface. The generated photovoltage tunes the Fermi level of the semiconducting CNT film in the FET through the electrostatic gate-coupling effect. Then, the optical response in the heterojunction can be efficiently coupled to the CNT channel and further amplified by the drain current. Spatially resolved photocurrent response measurements (Fig. 1 b) were obtained on an as-fabricated device to explore the working mechanism of the HGFETs. Obvious photocurrent generation only occurs when the laser beam irradiates the region covered by the CQD/ZnO heterojunction gate (HG); this result indicates that the HG plays a crucial role in establishing the built-in potential necessary to separate the photocarriers and generate a photovoltage for tuning the covered semiconducting CNT channel through the intermediate Y 2 O 3 gate insulator. As a highly selective optical response was observed only in the predefined photosensitive zone, the HGFET configuration provides significant advantages for minimizing electrical crosstalk between pixels in high-end applications, such as image sensors. Spectral responsivity measurements (Fig. 1 c) illustrate that the HGFET responds to light with wavelengths ranging from 600 nm to 1440 nm with a prominent peak at approximately 1300 nm, which is consistent with the absorption peak at 1286 nm in solution-processed PbS-halide CQDs (inset of Fig. 1 c). Opto-electric decoupling mechanism Opto-electric decoupling, i.e. , realizing optical sensing and electrical amplification at different regions, is the core goal of designing HGFETs with ultrahigh detectivity. To further elucidate the fundamental mechanism, we have presented a comparative analysis of the photoelectric conversion and primary noise components between the APD and HGFET structures (Fig. 1 d). In a typical APD with a p-doped absorption region and a lightly doped n-type multiplication region, the depletion region is established within the n-region and is intensified through reverse bias ( V bias ) to separate photoelectrons and induce avalanche multiplication for carrier multiplication 15 . The light absorption, charge separation, multiplication, and collection processes occur within the same semiconducting channel, which was named the opto-electric mixing structure; in this structure, noticeable excess noise, or amplified shot noise, arises from random ionization of carriers. The shot noise is generally expressed as I s =[2 qIM 2 F (M)] 1/2 , where M is the gain, I is the current for M = 1, q is the elementary charge, and F ( M ) is the excess noise factor typically exceeding unity 16 . Compared to a typical p-n junction photodiode, the shot noise in an APD is amplified by \(\:M\sqrt{F\left(M\right)}\) , which results in a proportionally lower signal-to-noise ratio. Additionally, fluctuations in thermally generated carriers (corresponding to thermal noise, I nt ) and fluctuations in carrier concentration related to traps or interface states (flicker noise, I nf ) can be amplified, although they may be negligible compared to the amplified shot noise under high electric field conditions. Therefore, compared to normal photodiodes, APDs exhibit no obvious advantage in terms of the signal-to-noise ratio for low-light-level imaging. To improve the signal-to-noise ratio of the detector, the HGFET was specially designed to operate with an opto-electric decoupling mechanism, i.e. , light absorption and photovoltage generation within the HG-based optical module, and photovoltage amplification and charge transport occur in the CNTs FET; the two components are separated by the Y 2 O 3 gate insulator. The optical response in the heterojunction can be efficiently coupled to the CNT channel and further amplified in the drain current through the electrostatic gate-coupling effect, and the photogain is primarily determined by the transconductance ( g m ) of the photovoltage-gated CNT FETs (as discussed in Supplementary Section 2). Additionally, since the p-i-n heterojunction operates in an open-circuit configuration, current-related noise, including shot noise or flicker noise, cannot be generated. As a result, only thermal noise is coupled into the device and amplified by the CNT FET. Due to the opto-electric decoupling design, the HGFET can amplify the photovoltage while barely amplifying the electrical noise, which significantly improved the signal-to-noise ratio and detectivity. Recently, various phototransistor-based infrared detectors have been reported based on trap-dominated photoconductive gain mechanisms (as depicted in Fig. S3) since photosensitive nanomaterials are directly grown on the semiconducting channel of FETs without an insulator layer 12, 13, 17, 22, 30 . Current-related noise, such as shot noise and flicker noise in these phototransistors, must be amplified, and carrier traps can be introduced to increase the flicker noise of the semiconducting channel. Thus, compared to InGaAs photodiodes, the detectivity of these phototransistors with the trap-dominated gain mechanisms was not greatly improved. Merits of the HGFET A typical fabricated HGFET infrared detector (Fig. 2 a) was characterized under preoptimized bias conditions ( V bg = -0.6 V, V ds = -0.1 V) to achieve high gains and low dark currents (Fig. S4). As shown in Fig. 2 b, the dynamic photocurrent responses were determined by increasing the irradiation power density ( P light ) from 0 to 15.4 W/cm 2 at 1300 nm. An obvious increase of 75.9 pA at background current (2.8 nA) indicates that the HGFET detector can respond to weak infrared radiation with a P light as low as 0.46 nW/cm 2 , corresponding to an irradiance of approximately 3007 photons/second. With increasing irradiation power density P light , the photocurrent I ph monotonically increases but follows a positive power function in the low P light region and a logarithmic function in the high P light region (Fig. 2 c and Supplementary Section 4). Notably, I ph does not show obvious saturation even at P light values as high as 15 W/cm 2 , which leads to a wide dynamic range (210 dB) in our HGFETs. For a photovoltage-gated HGFET (Fig. S5), the relationship between the open-circuit voltage ( \(\:{V}_{oc}\) ) of the p-i-n heterojunction and P light is expressed as follows: \(\:{V}_{oc}=\frac{{k}_{B}T}{q}ln\left(\frac{\eta\:qA{P}_{light}}{hv{I}_{0}}+1\right)\) (1), where \(\:{k}_{B}\) is the Boltzmann constant, \(\:T\) is the temperature, \(\:A\) is the optical area, \(\:{I}_{0}\) is the reverse saturation current, \(\:\eta\:\:\) is the external quantum efficiency, \(\:q\) is the elementary charge, and h ν is the energy of one photon. Then, the photocurrent \(\:{I}_{ph}\) of the HGFET can be determined as follows: \(\:\:{I}_{ph}=\frac{{g}_{m}\alpha\:{k}_{B}T}{q}ln\left(\frac{\eta\:qA{P}_{light}}{hv{I}_{0}}+1\right)\) (2), where α is the gate coupling coefficient between the HG and FET, and g m is the transconductance of the FET. Based on equations (1) and (2), a photoelectric response model of the HGFET was built and verified (see details in Section 4 of the supplementary information), which was also used to fit the measured photoresponse data for retrieving key parameters. Typically, we extracted HG parameters, such as η of 10%, from an ohmic contacted ZnO/CQD p-i-n photodiode with identical geometrical dimensions and structures (Fig. S7). The inherent gain ( \(\:G\) ) of the HGFET can be expressed as follows: \(\:G=Rhv/q\eta\:\) (3), where \(\:R=\frac{{I}_{ph}}{A{P}_{light}}\) is the photoresponsivity. Considering an R of up to 1.6×10 5 A/W with a V ds bias of -0.1 V under 1300 nm irradiation at P light of 0.46 nW/cm 2 (Fig. 2 c), the corresponding \(\:G\) is calculated to be ~ 1.5×10 6 . The response time of the HGFET detector is strongly dependent on the V ds applied to the CNT FET, as shown in Fig. 2 d, which demonstrates that increasing V ds from − 0.1 to -5 V results in a continuous decrease in the rise and decay times. The lowest rise time t Rise (95 µs) and fall time t Fall (415 µs) are achieved with a V ds bias of -5 V. According to the full photoelectric process of the HGFET shown in Fig. 1 d, the response time is dominated by two main processes, namely, the drift of photocarriers in the p-i-n heterojunction and the propagation delay in the CNT channel. The drift of photocarriers in the p-i-n heterojunction will occur at sub-microseconds, comparable to that of reported photodiodes with similar dimensions 28 , and CNT network FETs with a channel length of 10 µm typically exhibit a propagation delay of ~ 100 µs 31 . Therefore, the speed of the detector is mainly constrained by carrier transport in long-channel CNT FETs. The photocurrent decay is much slower than the photocurrent rise because the detrapping process of charged trap states is slower than the trapping process 32, 33 . To enable high-speed detection, the photocurrent rise and fall time should be further reduced through other strategies, such as adopting aligned CNTs, reducing the channel length, and applying an electric pulse at the gate to facilitate the escape of trapped carriers 12 . The current noise spectrum of the HGFET detector (see detailed measurements in the Supplementary Information and Fig. S8a) shows a typical 1/ f frequency-dependent character, indicating that the total current noise is mainly contributed by the flicker noise. As evidence, the calculated lines of shot noise and thermal noise (Supplementary Sections 5 and 8) are far below the measured curve of the noise spectrum, while the simulated flicker noise is almost consistent with the measured noise curve. Considering the opto-electronic decoupling mechanism of HGFETs, electric noise can be categorized into two sources: noise originating from the heterojunction and noise stemming from the underlying CNT FET (the developed noise model is detailed in Supplementary Section 8). In the open-circuit state, only the preexisting thermal noise ( V nT−HG ) of the heterojunction can be amplified by g m and then coupled to the detector. Compared to the flicker noise of the CNT FET, this noise is negligible (Fig. 2 e), which was determined by comparing the current noise of the device before and after depositing the p-i-n heterojunction on the high-κ layer of the CNT channel (Fig. S11). Based on the measured photoresponsivity R and electrical noise spectrum, the room-temperature specific detectivity ( D *) of the HGFET detector is plotted as a function of P light at 1300 nm (Fig. 2 e). D * increases with decreasing P light , and the peak value exceeds 10 14 Jones under weak light, which is recorded in all reported SWIR detections with measured noise data 3, 12, 13, 28 . Gate-tuneable operating mode of the HGFET The gain of the FET relies on the gate voltage, which will provide a factor to tune the detectivity of the HGFET detector. Figure 3 a displays the transfer curves of an HGFET under an infrared radiation power density ranging from 0 to 1.08 µW/cm² at 1300 nm. The threshold voltage ( V th ) shifts by approximately 0.16 V due to the photovoltage-gated response. The photocurrent for the HGFETs has a positive power function dependent on the light intensity (Fig. 3 b) when gated in the subthreshold region ( V bg =-0.05 to -0.15 V) but exhibits a logarithmic function (Fig. 3 c) when gated in the linear region ( V bg =-1.2 to -1.3 V). Further analysis (Figs. S9 and S10) was conducted to determine the V bg -dependent responsivity and gain (Fig. 3 d). Both the responsivity and gain increase with a power-law dependence on V bg in the subthreshold region and reach saturation at a V bg of approximately 0.5 V (see the fitted gain detailed in Supplementary Section 7); this is because the values are directly proportional to transconductance g m , which increases with V bg until the device enters the linear region. When operating in the linear region ( V bg ranging from − 1 to -2 V), a high inherent gain (~ 10 7 ) is achieved to amplify the photovoltage at the heterojunction of the HGFET in situ and provide a higher output current. The measured current noise of the HGFET is also dependent on V bg , which exhibits characteristics similar like the transfer characteristics of a CNT FET (Fig. 3 e). The relation between D * and V bg was extracted by combining the R - V bg curve in Fig. 3 d and the noise- V bg curve in Fig. 3 e, as shown in Fig. 3 f; these results demonstrate that the D * of the HGFET strongly depends on the gate voltage with a similar behaviour to that of the simulation results (see details in Supplementary Section 9 and Fig. S12). Corresponding to the operating region of the FET tuned by V bg , the HGFET can operate in two typical modes, i.e. , high-gain mode (in the linear region) and high-detectivity mode (in the subthreshold region). In high-gain mode, the HGFET detector can provide a high output current, which is beneficial for simplifying the readout circuit design. In high detectivity mode, the HGFET detector can provide high sensitivity for weak light detection with low power dissipation. Performance comparison and benchmarking We compared the performance of the HGFET detector and a commercial InGaAs photodiode (FGA015) 34 by directly testing the SWIR response characteristics under the same testing conditions (see details in Supplementary Section 10). Figure 4 a illustrates the detailed measurement system, enabling precise photoelectric testing and laser beam analysis. The output beam spot can be adjusted using two different objective lenses with amplification factors of 10× and 50× to match the optical areas of the two devices. The output power was modulated using adjustable slots and neutral density filters, and it was meticulously calibrated using a germanium power metre and a standard InGaAs photodiode (Table S1 ). The time-resolved photoresponses under weak infrared irradiation at 1300 nm (Fig. 4 b) show that the HGFET demonstrates a high SNR ( I ph / I n ) (approximately 70) at a light intensity as low as 0.46 nW/cm 2 , at which the InGaAs photodiode exhibits no response. As the InGaAs photodiode begins to show a weak current response (with an SNR of approximately 7), the light intensity increases to 3.78 nW/cm 2 . The photocurrent in the HGFET device (in the subthreshold region) exhibited a clear power-law relationship with the incident light intensity (Fig. 4 c), even when the power intensity was below 1 nW/cm 2 . However, the photocurrent in the InGaAs photodiode exhibits a linear relation with the light intensity and begins to deviate from the linear relation as the light intensity decreases below 100 nW/cm 2 ; these results indicate that the responsivity is uncertain under weak light, mainly owing to the absence of inherent gain-induced low R (Fig. 4 c and 4 d). To preliminarily demonstrate the array ability of the HGFET detectors for passive night vision imaging, we fabricated an image sensor featuring 64×64 pixels of HGFETs, and the pixel array was connected to the readout circuits on the printed circuit board (PCB, see details in Supplementary Section 11). Without an image lens, we displayed the “PKU” images acquired at different irradiation power densities using an assembled test system (Fig. 4 e). Despite far from optimizing device structure (lack of a gate switch transistor for each pixel and non-ideal electrical cross-talk within each row of the 64 pixels), the HGFET imager successfully captured the “PKU” pattern (Fig. 4 f) at a low power density (100 nW/cm²), demonstrating the potential of HGFET for high sensitivity. We performed benchmarking tests for our HGFET detector using commercial photodiodes and other thin-film-based infrared photodetectors, focusing on important metrics such as specific detectivity and speed. In Fig. 5 a, the wavelength-dependent D * characteristics of our HGFET device are compared with those of InGaAs photodiodes (from Thorlabs and Hamamatsu) and Ge photodiodes (from Thorlabs) measured under identical setup and conditions. The HGFET achieved a peak D * that exceeded 10 14 Jones, which is nearly two orders of magnitude greater than that of InGaAs photodiodes. This is the highest reported peak D * for thin-film-based photodetectors in the SWIR range, facilitating detection under moonlight and even starlight conditions, as depicted in Fig. 5 b and detailed in Table S2 34, 35 . Moreover, the sensitivity of HGFETs can be substantially improved by optimizing the EQE of the CQD heterojunction and enhancing the gate efficiency of the FET; thus, it is possible to approach the fundamental limits defined by the signal fluctuation limit (SFL) and background limited infrared photodetection (BLIP) of approximately 10 18 Jones at 1300 nm 5 . Similar to all reported electrical devices with internal gain 17 , a trade-off occurs between the gain ( G ) and bandwidth in photodetectors, including the HGFET, and the gain-bandwidth ( GBW ) product is the key metric for characterizing the comprehensive performance in terms of the sensitivity and speed of a photodetector with gain. Figure 5 c presents the GBWs of five typical detectors with different architectures, including photoconductors 36 , photodiodes 18, 34 , APDs 26, 27 , photogating devices 12 , and HGFETs. A maximum GBW of 15.5 GHz was achieved in the HGFET with randomly oriented CNT films, which outperforms all reported thin-film-based infrared detectors and InGaAs PIN diodes 13, 18, 25, 28 (Fig. S20). With the much higher carrier mobility than randomly oriented CNT film, aligned semiconducting CNT films have been considered as a superior semiconducting channel in constructing FETs with high g m and speed 38 . Thus, the HGFET based on aligned CNTs exhibits a GBW of up to 69.2 THz alongside a D * of 6.7×10 13 Jones (Figs. S20 and S21) and far exceeds that of all existing infrared detectors, including the latest advanced APD devices 13, 26, 27 . This outstanding GBW performance of the HGFET primarily results from the physical mechanism of opto-electric decoupling, specifically rapid photocarrier separation facilitated by the built-in potential, ultrafast electrostatic coupling, swift charge transport within the CNT channel, and excellent signal amplification capability of the CNT FET. Opto-electrical decoupling enables HGFETs provide greater controllability and can help alleviate trade-offs between photon absorption and electrical noise, as well as between gain and response speed. Excellent optical and electrical properties can be achieved simultaneously in one device by employing two solution-processed semiconductors rather than relying on single-crystalline materials that necessitate precise lattice matching; this process may promote the monolithic integration of HGFET detector arrays with silicon ROICs through a back end of line (BEOL)-compatible process. Furthermore, HGFETs can replace the light absorber and serve as a versatile platform for photodetection across various wavelength bands; thus, the detector can be adapted to different optical applications. Conclusion We have reported an opto-electric decoupling HGFET SWIR detector that presents a high inherent gain for amplifying signals while barely amplifying noise for detecting weak infrared radiation. The HGFET devices exhibit a recorded detectivity of 1.27×10 14 Jones and a maximum gain-bandwidth product of 69.2 THz to 1300 nm irradiation at room temperature. The opto-electric decoupling device can detect weak infrared radiation of 0.46 nW/cm 2 , which is much more sensitive than the commercial and all reported SWIR detectors and especially enables a starlight detection or vision. As the fabrication process of HGFET is highly compatible with CMOS readout integrated circuits, the HGFET offers a universal platform for achieving high-end passive night vision image sensors in thin-film semiconductors; this technology paves the way for innovative optoelectronic circuits and future monolithically integrated systems with high resolution, high sensitivity and low cost. Methods Materials preparation Polymer-sorted, solution-derived CNTs with a semiconductor purity exceeding 99.999% were prepared using dispersion and centrifugation, as detailed previously in the literature 37 . The polymer-wrapped CNT solution was then diluted with toluene. Randomly oriented CNT films with high uniformity were formed by immersing the cleaned substrate in a diluted CNT solution for 48 hours. A dimension-limited self-alignment (DLSA) procedure was employed to deposit aligned CNT films, as previously described in the literature 38 . Next, a cleaning process involving coating with yttrium oxide (Y 2 O 3 ) and then decoating to remove the polymer was carried out. Finally, thermal annealing was conducted at 600°C in an Ar/H 2 atmosphere. The synthesis of PbS CQDs with oleylamine ligands was executed following a solution-processed procedure detailed in prior studies 28, 29 . In the ambient atmosphere, a solution-phase ligand exchange process was conducted to synthesize PbS-halide CQDs. These CQDs were then dispersed in a mixture of amylamine, hexylamine, and butylamine (in a volume ratio of 3:2:10) at a concentration of 150 mg/mL to prepare the PbS-halide CQD ink for film fabrication. The construction of the ZnO/PbS CQD heterojunction began with the sputtering of a 40 nm-thick ZnO thin film utilizing a previously described method 39 . Next, a 150 nm thick absorbing layer was deposited onto the ZnO thin film via spin coating the PbS-halide CQD ink at 2500 rpm for 20 seconds. The final step involved depositing two layers of PbS CQDs treated with 1,2-ethanedithiol (EDT, 0.02 vol% in an acetonitrile solution) to serve as the p-doped layer. The doping concentrations of the prepared ZnO film and PbS-EDT CQDs were previously measured to be ~ 10 17 cm − 3 . HGFET fabrication The HGFET detectors were constructed on Si/SiO 2 substrates. As illustrated in Fig. S2, the local bottom-gate metal was patterned using photolithography and electron beam evaporation (EBE) of a Ti/Pd film (1/20 nm) via a standard lift-off process. A 10 nm thick (100 cycles) layer of hafnium oxide (HfO 2 ) dielectric was deposited onto the gate metal using atomic layer deposition. Subsequently, a CNT film was deposited onto the HfO 2 dielectric and patterned through photolithography and reactive ion etching (RIE) to create the channel region. Source ( S ) and drain ( D ) pads were then created through photolithography, EBE of a Ti/Pd/Au film (0.3/40/30 nm), followed by a standard lift-off process. An ultrathin Y 2 O 3 layer (~ 6 nm) was deposited on the CNT channel through thermal oxidation at 270 ℃ in air, serving as the dielectric for the floating gate. Finally, the p-i-n heterojunction was constructed by sequentially depositing the ZnO film, PbS-halide CQD film, and PbS-EDT CQD film. HGFET imager fabrication The fabrication process, as illustrated in Fig. S15, began with the deposition of a randomly oriented CNT film on a 4-inch Si/SiO 2 substrate, followed by patterning using photolithography and RIE. Next, the source/drain electrodes and the lower interconnect line were patterned by photolithography, followed by EBE of a 30 nm Pd film and subsequent lift-off processing. An isolation layer of 60 nm SiO 2 was deposited using photolithography, EBE, and a subsequent lift-off process. The upper interconnect line was then formed by photolithography and deposition of a 20/600 nm Ti/Au film via EBE. Following this procedure, similar steps were performed to deposit the ultrathin Y 2 O 3 layer and p-i-n heterojunction. Finally, an HGFET array with 64×64 pixels was constructed and wire bonded to the readout circuit board. Characterization of the materials and device SEM images were obtained using a FEI ZEISS Sigma 300 scanning electron microscope. The optical absorption spectra of the PbS CQDs were measured with a UV-3600 plus spectrophotometer. The Raman spectrum of the CNT film was collected by a LabRAM HR800 instrument (Jobin-Yvonr). Optoelectronic measurements of the HGFET devices and the InGaAs diode were conducted using the measurement system depicted in Fig. 4 a. A supercontinuous spectrum laser from the NKT Company was utilized to characterize the device responses, with the laser wavelength adjustable from 640 to 2100 nm. The spectral responsivity of the devices was assessed using a monochromator and calibrated against a standard InGaAs diode (FGA21, Thorlabs). Photocurrent spectroscopy was performed using an SR830 lock-in amplifier in conjunction with an SR540 chopper and a tungsten lamp equipped with monochromator, all of which were controlled by a LabVIEW program. The transient response and − 3 dB bandwidth were measured using a high-speed oscilloscope (Agilent DSO7054A). Current noise spectra were obtained using the PDA FS380 (Bodawei Electronic Technology Co., Ltd.) and E4727B (Keysight Technologies Co., Ltd.) systems. All electronic transport measurements were carried out using a Keithley 4200 semiconductor analyser at room temperature under ambient conditions. Image capture A schematic diagram of the assembled test system is shown in Fig. 4 e. The setup involves collimated infrared light emitted from a 940 nm LED source (M940L3-C4 from Thorlabs) with a beam diameter of 44 mm. The power density of the light was modulated using neutral density filters. A photomask containing the designed patterns was used to provide a spatial light distribution, which was subsequently captured by the 64×64 pixel HGFET imager. Detector characteristics The calculated gain of the HGFET, as outlined in Section 2 (Supporting Information), is directly linked to the transconductance ( g m ). The calculated photocurrent, which was described in Section 4, exhibits a positive power function in the subthreshold region of the CNT FET and a logarithmic function in the linear region. These distinctive response characteristics were further validated by comparing the extracted g m and subthreshold swing ( SS ) of HGFETs with those of top metal-gated CNT FETs. TCAD simulations were constructed and illustrated a continuously fitted photocurrent under various irradiation conditions (refer to Fig. S7). The specific parameters used for the TCAD simulation are detailed in Section 4. The noise characteristics are described in Section 8, and the calculated expressions for the HGFET noise are provided. The detectivity characteristics of HGFETs are presented in Section 9, illustrating how the signal-to-noise ratio (SNR) is proportional to g m / I ds in the subthreshold region and g m 2 / I ds in the linear region. Declarations Data availability. The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request. Acknowledgements This work is supported by the Natural Science Foundation of China (62225101 and U21A6004) and the Peking Nanofab Laboratory. Author contributions Z.Z. and Y.W. advised on and led this project. S. Z. carried out the device fabrication and experimental measurements. X. Z. carried out the aligned CNT-based HGFET fabrication and measurements. S.Z. and P.Z. provided the TCAD simulation. D.L. and J.J. designed and provided the readout circuit boards. L. X. and D. Z. synthesized the PbS CQDs and fabricated the CQDs photodiodes. S.Z., Y.W., and Z.Z. wrote the paper. All authors discussed the results and prepared and commented on the manuscript. Competing interests The authors declare no competing interests. Additional information The supplementary material is contained. References 1. Xia F., Wang H., Di Xiao, Dubey M. & Ramasubramaniam A. Two-dimensional material nanophotonics. Nat. Photonics . 12 , 899–907 (2014). 2. Saran R. & Curry R. J. 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Supplementary Files SISYzhouHGFETforweakinfraredradiationdetection20240708.docx Cite Share Download PDF Status: Under Review Version 1 posted 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-4705743","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":331665439,"identity":"7ec7c4e7-759d-40c1-be16-7868471598ce","order_by":0,"name":"Zhiyong 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13:00:38","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4705743/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4705743/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":61809383,"identity":"52a5f3b9-a2ea-4e20-9664-2aec29622b66","added_by":"auto","created_at":"2024-08-05 20:15:12","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":7001688,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-4705743/v1/97180db8e675eae474c39d69.png"},{"id":61810927,"identity":"889a444a-f400-499e-98d5-f9010cc5a3f5","added_by":"auto","created_at":"2024-08-05 20:23:12","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1363202,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePerformance of the HGFET under 1300 nm irradiation at a constant bottom-gate voltage of -0.6 V. a,\u003c/strong\u003e Schematic of the electrical circuit showing the voltage bias. \u003cem\u003eV\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e, source–drain voltage; \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e, bottom gate–source voltage. \u003cstrong\u003eb,\u003c/strong\u003e Time-resolved photoresponse at a \u003cem\u003eV\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e of -0.1 V. Inset: the rescaled response curve of the area framed by the dashed rectangle. \u003cstrong\u003ec,\u003c/strong\u003e Extracted intensity-dependent photocurrent and responsivity. The fitted photocurrent based on the HGFET model is included, describing the response mechanism. \u003cstrong\u003ed,\u003c/strong\u003e Response time as a function of drain-source voltage, indicating that the HGFET speed is influenced by the transit time of holes in the CNT channel. Inset: the normalized response at \u003cem\u003eV\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e=-5 V showing rise and fall times of 95 µs and 415 µs, respectively. \u003cstrong\u003ee,\u003c/strong\u003e Measured current noise of the HGFET as a function of frequency at \u003cem\u003eV\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e=-0.1 V and \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e=-0.6 V. The calculated shot noise, 1/\u003cem\u003ef \u003c/em\u003enoise and thermal noise (including the thermal noise of the FET and the thermal noise amplified by the FET from the heterojunction). The dynamic resistance of the p-i-n junction, \u003cem\u003eR\u003c/em\u003e\u003csub\u003eHG\u003c/sub\u003e~6 GΩ) limit is also included for reference. \u003cstrong\u003ef,\u003c/strong\u003e Specific detectivity (\u003cem\u003eD\u003c/em\u003e*) at room temperature.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-4705743/v1/28022416ca7546651ced6930.png"},{"id":61809385,"identity":"90d62768-81fc-4409-8593-8b57f3da8957","added_by":"auto","created_at":"2024-08-05 20:15:12","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1082654,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eGate-tuneable response characteristics of the HGFET detector under 1300 nm irradiation. a,\u003c/strong\u003e Transfer characteristics of the HGFET with increasing power density. \u003cstrong\u003eb,\u003c/strong\u003e Extracted photocurrent of three typical HGFETs with \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e values of -0.05 V, -0.10 V, and -0.15 V, ensuring that the devices operated within the subthreshold region. Each device underwent three repeated measurements. The dashed lines represent the fitting results based on the photovoltage-gated FET model. \u003cstrong\u003ec,\u003c/strong\u003e Extracted photocurrent of the same devices in figure \u003cstrong\u003eb \u003c/strong\u003ewith \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e of -1.20 V, -1.25 V, and -1.30 V, making them operate within the linear region. \u003cstrong\u003ed,\u003c/strong\u003e Extracted \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e-dominated photoresponsivity (top) and gain (bottom) at power densities of 0.46, 12.04 and 247.71 nW/cm\u003csup\u003e2\u003c/sup\u003e. The solid green line represents the gain fitted by the photovoltage-gated FET model (Supplementary Section 7). \u003cstrong\u003ee,\u003c/strong\u003e Measured current noise of the HGFET device at different \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e values using two test systems (PDA FS380 in blue and E4727B in black). \u003cstrong\u003ef,\u003c/strong\u003e Extracted \u003cem\u003eD\u003c/em\u003e* at different \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg \u003c/sub\u003evalues, showing a peak value when the HGFET is operated in the subthreshold region.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-4705743/v1/20f126bda34231bed668e315.png"},{"id":61809387,"identity":"a758731b-c312-43d9-86ee-edbd861ba0b6","added_by":"auto","created_at":"2024-08-05 20:15:12","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":13783606,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eComparison of the performance of the InGaAs photodiode and HGFET. a,\u003c/strong\u003e Schematic illustration of the measurement system: Monochromatic light from the spectrometer is modulated using adjustable slots and neutral density filters, and its output power is calibrated with a germanium power metre (PM 100D, Thorlabs) and a standard InGaAs photodiode (FGA21, Thorlabs). The size of the output beam spot can be altered using one of two objective lenses, providing amplification factors of 10× and 50×. Optoelectronic measurements of the photodetectors were conducted using a probe station connected to a semiconductor parameter analyser (Keithley 4200). The size and intensity profile of the output beam spot are characterized by capturing the reflected light with a standard InGaAs camera (First Light Vision C-Red3). \u003cstrong\u003eb,\u003c/strong\u003e Time-resolved photoresponse of an HGFET (top) and an FGA015 InGaAs diode (middle) under different irradiation power densities at 1300 nm (illustrated in the bottom panel). \u003cstrong\u003ec-d,\u003c/strong\u003e Extracted intensity-dependent photocurrent (top) and responsivity (bottom) of the HGFET (\u003cstrong\u003ec\u003c/strong\u003e) at \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e=-0.6 V and \u003cem\u003eV\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e=-0.1 V and FGA015 (\u003cstrong\u003ed\u003c/strong\u003e) at \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebias\u003c/sub\u003e=-5 V. The black dashed line shows the fitting curve based on the HGFET model or the photodiode model.\u003cstrong\u003e e,\u003c/strong\u003e Schematic diagram of the assembled image sensor test system. The collimated infrared light with a beam diameter of 44 mm (wavelength of 940 nm, LED source M940L3-C4 from Thorlabs) is modulated by neutral density attenuators. A photomask with designed patterns is employed to provide spatial light distribution on the HGFET. The image information is read and displayed on a computer screen. \u003cstrong\u003ef,\u003c/strong\u003e Images of the ‘PKU’ pattern captured under various power densities.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-4705743/v1/4621eec6c413401f147ce750.png"},{"id":61809386,"identity":"82b05911-34e5-436b-9d0d-7d570cec4556","added_by":"auto","created_at":"2024-08-05 20:15:12","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":682229,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eBenchmarking HGFET, InGaAs diodes and other thin-film photodetectors. a,\u003c/strong\u003e Comparison of the room temperature-specific detectivity \u003cem\u003eD\u003c/em\u003e* between the HGFET and commercial photodiodes. \u003cstrong\u003eb,\u003c/strong\u003e Comparison of the detectable light intensity and detectivity (\u003cem\u003eD\u003c/em\u003e*) between the HGFET and other reported thin-film-based infrared detectors (detailed in Table S2). \u003cstrong\u003ec, \u003c/strong\u003eGain-frequency plot for different detector architectures. The dashed red and blue lines represent the typical magnitude order of the gain-bandwidth product for the randomly oriented CNT HGFET (channel length and width of 10/10 μm, \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e=-1.2 V and \u003cem\u003eV\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e=-5 V) and aligned CNT HGFET (channel length and width of 2/10 μm, \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e=-2 V and \u003cem\u003eV\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e=-0.1 V), respectively.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-4705743/v1/5dfbf5e8ddfa58cc1ef381d8.png"},{"id":61811794,"identity":"d6a8e12d-fe85-4116-93fd-41fb5e8940f1","added_by":"auto","created_at":"2024-08-05 20:31:35","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":28629230,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4705743/v1/021e007e-34ef-40e4-a71a-63ce750d231e.pdf"},{"id":61809388,"identity":"906b6eb4-2a59-4c11-ab7a-af690f1cfd4d","added_by":"auto","created_at":"2024-08-05 20:15:12","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":37802123,"visible":true,"origin":"","legend":"","description":"","filename":"SISYzhouHGFETforweakinfraredradiationdetection20240708.docx","url":"https://assets-eu.researchsquare.com/files/rs-4705743/v1/62063ca732ca2091b146ae0f.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Opto-electrical decoupled phototransistor for starlight detection","fulltext":[{"header":"Introduction","content":"\u003cp\u003eExtensive efforts have been dedicated to improving the detectivity and resolution of shortwave infrared (SWIR, within the band of 0.9\u0026ndash;1.7 \u0026micro;m) photodetectors, which enable remote imaging, night vision, spectroscopy and object tracing\u003csup\u003e1\u0026ndash;4\u003c/sup\u003e. Generally, the detection of weak infrared radiation (typically below 10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e W\u0026middot;Sr\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u0026middot;\u0026micro;m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) places extremely high demands on the signal-to-noise ratio (SNR), also known as the detectivity of sensors; due to these demands, it is necessary to achieve high optical responses and low electrical noise\u003csup\u003e5\u003c/sup\u003e. Mainstream SWIR detectors rely on the diode configuration and are currently dominated by epitaxial semiconductors, such as indium gallium arsenide (InGaAs); through continuously improving material and interface quality, researchers have developed detectors with high specific detectivity (~\u0026thinsp;10\u003csup\u003e13\u003c/sup\u003e Jones) based on an ultralow dark current below 1 nA/cm\u003csup\u003e2\u003c/sup\u003e and electrical noise approaching the technological limit\u003csup\u003e5\u0026ndash;8\u003c/sup\u003e. The optical response of a diode detector is determined by the external quantum efficiency (EQE), which can reach as high as ~\u0026thinsp;90%\u003csup\u003e5\u003c/sup\u003e; thus, there is little room for improvement. Further improving the detectivity beyond 10\u003csup\u003e13\u003c/sup\u003e Jones, which enables the detection of weak infrared radiation at sub-1 nW/cm\u003csup\u003e2\u003c/sup\u003e levels (starlight)\u003csup\u003e9\u003c/sup\u003e, is challenging in a photodiode structure that lacks inherent gain and provides only one pair of carriers per single incident photon\u003csup\u003e5, 10\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eImplementing an inherent gain mechanism is essential for enhancing the optical response, as exemplified in device architectures, such as avalanche photodiodes (APDs) and nanostructured field-effect transistors (FETs)\u003csup\u003e11\u0026ndash;13\u003c/sup\u003e. Under a high electric field, photocarriers in APDs are accelerated and multiplied through impact ionization, achieving a high gain (\u003cem\u003eM\u003c/em\u003e) that exceeds 10\u003csup\u003e5\u003c/sup\u003e when operating in Geiger mode for single-photon detection\u003csup\u003e14, 15\u003c/sup\u003e. However, due to the random ionization of charge carriers, APDs tend to exhibit significantly amplified excess noise \u003csup\u003e11, 16\u003c/sup\u003e. Emerging nanomaterials with facile solution processability and integration capability offer greater flexibility in infrared detector design, holding significant potential for constructing novel detectors with high gain and low costs\u003csup\u003e1, 2\u003c/sup\u003e. Recently, extensive infrared radiation detectors with nanostructured FET architectures have been reported to have inherent gains\u003csup\u003e17\u0026ndash;21\u003c/sup\u003e. Quantum dot-sensitized graphene FET, a typical type of nanostructured phototransistor, achieved high photogain (up to 10\u003csup\u003e8\u003c/sup\u003e) based on a trap-dominated photogating effect, but usually suffers from high dark current, noise levels, and limited response speed\u003csup\u003e9, 12\u003c/sup\u003e. More recently, researchers have also reported sensitized FETs based on large bandgap semiconductor channel materials with reduced dark current (0.1\u0026ndash;100 nA) and high photogain\u003csup\u003e18, 22\u0026ndash;24\u003c/sup\u003e. Almost all the reported FET detectors with high inherent gain have also been no substantial breakthrough in detectivity, since the noise and signal are simultaneously amplified in the same channel in charge of optical sensing and electrical amplification. Therefore, a SWIR detector with a well-designed device structure and operating mechanism is highly desired to achieve opto-electric decoupling, facilitating ultrahigh detectivity beyond 10\u003csup\u003e13\u003c/sup\u003e Jones and enabling passive starlight detection or vision.\u003c/p\u003e \u003cp\u003eIn this work, we present a heterojunction-gated field-effect transistor (HGFET) that achieves ultrahigh photogain and exceptionally low noise in the SWIR region, benefiting from a design that incorporates a comprehensive opto-electric decoupling mechanism. The stacked heterojunction absorbs infrared radiation and separates electron-hole pairs. Then, the generated photovoltage tunes the drain current of the CNT FET through an electrostatic gate coupling effect. As a result, optical sensing process and electrical amplification process are completely isolated in space. The opto-electric decoupling HGFET significantly detected and amplified SWIR signals with a high inherent gain of 1.5\u0026times;10\u003csup\u003e6\u003c/sup\u003e while barely amplifying noise; in addition, the HGFET exhibited a recorded specific detectivity above 10\u003csup\u003e14\u003c/sup\u003e Jones at 1300 nm and a maximum gain-bandwidth product (\u003cem\u003eGBW\u003c/em\u003e) of 15.5 GHz, enabling the detection of weak infrared radiation at 0.46 nW/cm\u003csup\u003e2\u003c/sup\u003e. The use of aligned CNTs in HGFETs further promoted the \u003cem\u003eGBW\u003c/em\u003e to 69.2 THz, surpassing the theoretical limit of sensitized Si FETs and state-of-the-art InGaAs APDs\u003csup\u003e18, 25\u0026ndash;27\u003c/sup\u003e. The results demonstrated that the HGFET is a promising SWIR detector for realizing high-end passive night vision image sensors with high resolution, high sensitivity, and low cost.\u003c/p\u003e"},{"header":"HGFET structure","content":"\u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea shows a schematic of the HGFET infrared detector, which consists of a CNT thin-film transistor gated by a PbS CQD/ZnO heterojunction (the detailed fabrication processes are provided in Methods and Supplementary Section 1). Local bottom-gated metal-oxide- semiconductor (MOS) FETs are fabricated on a randomly oriented semiconducting CNT film covered by an yttrium oxide (Y\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) film which acts as gate insulator to separate the photoelectric conversion component above and the electronic component below. A sputtered 40-nm layer of n-doped ZnO (with a dopant concentration of ~\u0026thinsp;10\u003csup\u003e17\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e)\u003csup\u003e28, 29\u003c/sup\u003e is deposited and patterned on a Y\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/CNT film channel through photolithography and a lift-off process. A 150 nm-thick intrinsic PbS-halide CQD layer and a 30 nm-thick ethanedithiol (EDT)-treated p-doped PbS CQD layer (with a dopant concentration of 10\u003csup\u003e17\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e) are spin-cast to form a p-i-n heterojunction, which generates a negative photovoltage through the absorption of infrared photons, the separation of photogenerated electron-hole pairs through the built-in field, and the accumulation of electrons at the ZnO/gate dielectric interface. The generated photovoltage tunes the Fermi level of the semiconducting CNT film in the FET through the electrostatic gate-coupling effect. Then, the optical response in the heterojunction can be efficiently coupled to the CNT channel and further amplified by the drain current.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSpatially resolved photocurrent response measurements (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb) were obtained on an as-fabricated device to explore the working mechanism of the HGFETs. Obvious photocurrent generation only occurs when the laser beam irradiates the region covered by the CQD/ZnO heterojunction gate (HG); this result indicates that the HG plays a crucial role in establishing the built-in potential necessary to separate the photocarriers and generate a photovoltage for tuning the covered semiconducting CNT channel through the intermediate Y\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e gate insulator. As a highly selective optical response was observed only in the predefined photosensitive zone, the HGFET configuration provides significant advantages for minimizing electrical crosstalk between pixels in high-end applications, such as image sensors. Spectral responsivity measurements (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec) illustrate that the HGFET responds to light with wavelengths ranging from 600 nm to 1440 nm with a prominent peak at approximately 1300 nm, which is consistent with the absorption peak at 1286 nm in solution-processed PbS-halide CQDs (inset of Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec).\u003c/p\u003e"},{"header":"Opto-electric decoupling mechanism","content":"\u003cp\u003eOpto-electric decoupling, \u003cem\u003ei.e.\u003c/em\u003e, realizing optical sensing and electrical amplification at different regions, is the core goal of designing HGFETs with ultrahigh detectivity. To further elucidate the fundamental mechanism, we have presented a comparative analysis of the photoelectric conversion and primary noise components between the APD and HGFET structures (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). In a typical APD with a p-doped absorption region and a lightly doped n-type multiplication region, the depletion region is established within the n-region and is intensified through reverse bias (\u003cem\u003eV\u003c/em\u003e\u003csub\u003ebias\u003c/sub\u003e) to separate photoelectrons and induce avalanche multiplication for carrier multiplication\u003csup\u003e15\u003c/sup\u003e. The light absorption, charge separation, multiplication, and collection processes occur within the same semiconducting channel, which was named the opto-electric mixing structure; in this structure, noticeable excess noise, or amplified shot noise, arises from random ionization of carriers. The shot noise is generally expressed as \u003cem\u003eI\u003c/em\u003e\u003csub\u003es\u003c/sub\u003e=[2\u003cem\u003eqIM\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e\u003cem\u003eF\u003c/em\u003e(M)]\u003csup\u003e1/2\u003c/sup\u003e, where \u003cem\u003eM\u003c/em\u003e is the gain, \u003cem\u003eI\u003c/em\u003e is the current for \u003cem\u003eM\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1, \u003cem\u003eq\u003c/em\u003e is the elementary charge, and \u003cem\u003eF\u003c/em\u003e(\u003cem\u003eM\u003c/em\u003e) is the excess noise factor typically exceeding unity\u003csup\u003e16\u003c/sup\u003e. Compared to a typical p-n junction photodiode, the shot noise in an APD is amplified by \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:M\\sqrt{F\\left(M\\right)}\\)\u003c/span\u003e\u003c/span\u003e, which results in a proportionally lower signal-to-noise ratio. Additionally, fluctuations in thermally generated carriers (corresponding to thermal noise, \u003cem\u003eI\u003c/em\u003e\u003csub\u003ent\u003c/sub\u003e) and fluctuations in carrier concentration related to traps or interface states (flicker noise, \u003cem\u003eI\u003c/em\u003e\u003csub\u003enf\u003c/sub\u003e) can be amplified, although they may be negligible compared to the amplified shot noise under high electric field conditions. Therefore, compared to normal photodiodes, APDs exhibit no obvious advantage in terms of the signal-to-noise ratio for low-light-level imaging.\u003c/p\u003e \u003cp\u003eTo improve the signal-to-noise ratio of the detector, the HGFET was specially designed to operate with an opto-electric decoupling mechanism, \u003cem\u003ei.e.\u003c/em\u003e, light absorption and photovoltage generation within the HG-based optical module, and photovoltage amplification and charge transport occur in the CNTs FET; the two components are separated by the Y\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e gate insulator. The optical response in the heterojunction can be efficiently coupled to the CNT channel and further amplified in the drain current through the electrostatic gate-coupling effect, and the photogain is primarily determined by the transconductance (\u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e) of the photovoltage-gated CNT FETs (as discussed in Supplementary Section 2). Additionally, since the p-i-n heterojunction operates in an open-circuit configuration, current-related noise, including shot noise or flicker noise, cannot be generated. As a result, only thermal noise is coupled into the device and amplified by the CNT FET. Due to the opto-electric decoupling design, the HGFET can amplify the photovoltage while barely amplifying the electrical noise, which significantly improved the signal-to-noise ratio and detectivity. Recently, various phototransistor-based infrared detectors have been reported based on trap-dominated photoconductive gain mechanisms (as depicted in Fig. S3) since photosensitive nanomaterials are directly grown on the semiconducting channel of FETs without an insulator layer\u003csup\u003e12, 13, 17, 22, 30\u003c/sup\u003e. Current-related noise, such as shot noise and flicker noise in these phototransistors, must be amplified, and carrier traps can be introduced to increase the flicker noise of the semiconducting channel. Thus, compared to InGaAs photodiodes, the detectivity of these phototransistors with the trap-dominated gain mechanisms was not greatly improved.\u003c/p\u003e"},{"header":"Merits of the HGFET","content":"\u003cp\u003eA typical fabricated HGFET infrared detector (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea) was characterized under preoptimized bias conditions (\u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e= -0.6 V, \u003cem\u003eV\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e= -0.1 V) to achieve high gains and low dark currents (Fig. S4). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, the dynamic photocurrent responses were determined by increasing the irradiation power density (\u003cem\u003eP\u003c/em\u003e\u003csub\u003elight\u003c/sub\u003e) from 0 to 15.4 W/cm\u003csup\u003e2\u003c/sup\u003e at 1300 nm. An obvious increase of 75.9 pA at background current (2.8 nA) indicates that the HGFET detector can respond to weak infrared radiation with a \u003cem\u003eP\u003c/em\u003e\u003csub\u003elight\u003c/sub\u003e as low as 0.46 nW/cm\u003csup\u003e2\u003c/sup\u003e, corresponding to an irradiance of approximately 3007 photons/second. With increasing irradiation power density \u003cem\u003eP\u003c/em\u003e\u003csub\u003elight\u003c/sub\u003e, the photocurrent \u003cem\u003eI\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e monotonically increases but follows a positive power function in the low \u003cem\u003eP\u003c/em\u003e\u003csub\u003elight\u003c/sub\u003e region and a logarithmic function in the high \u003cem\u003eP\u003c/em\u003e\u003csub\u003elight\u003c/sub\u003e region (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec and Supplementary Section 4). Notably, \u003cem\u003eI\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e does not show obvious saturation even at \u003cem\u003eP\u003c/em\u003e\u003csub\u003elight\u003c/sub\u003e values as high as 15 W/cm\u003csup\u003e2\u003c/sup\u003e, which leads to a wide dynamic range (210 dB) in our HGFETs.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFor a photovoltage-gated HGFET (Fig. S5), the relationship between the open-circuit voltage (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{V}_{oc}\\)\u003c/span\u003e\u003c/span\u003e) of the p-i-n heterojunction and \u003cem\u003eP\u003c/em\u003e\u003csub\u003elight\u003c/sub\u003e is expressed as follows:\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:{V}_{oc}=\\frac{{k}_{B}T}{q}ln\\left(\\frac{\\eta\\:qA{P}_{light}}{hv{I}_{0}}+1\\right)\\)\u003c/span\u003e \u003c/span\u003e (1),\u003c/p\u003e \u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{k}_{B}\\)\u003c/span\u003e\u003c/span\u003e is the Boltzmann constant, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:T\\)\u003c/span\u003e\u003c/span\u003e is the temperature, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:A\\)\u003c/span\u003e\u003c/span\u003e is the optical area, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{I}_{0}\\)\u003c/span\u003e\u003c/span\u003e is the reverse saturation current, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\eta\\:\\:\\)\u003c/span\u003e\u003c/span\u003eis the external quantum efficiency, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:q\\)\u003c/span\u003e\u003c/span\u003e is the elementary charge, and \u003cem\u003eh\u003c/em\u003eν is the energy of one photon. Then, the photocurrent \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{I}_{ph}\\)\u003c/span\u003e\u003c/span\u003e of the HGFET can be determined as follows:\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:\\:{I}_{ph}=\\frac{{g}_{m}\\alpha\\:{k}_{B}T}{q}ln\\left(\\frac{\\eta\\:qA{P}_{light}}{hv{I}_{0}}+1\\right)\\)\u003c/span\u003e \u003c/span\u003e(2),\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eα\u003c/em\u003e is the gate coupling coefficient between the HG and FET, and \u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e is the transconductance of the FET. Based on equations (1) and (2), a photoelectric response model of the HGFET was built and verified (see details in Section 4 of the supplementary information), which was also used to fit the measured photoresponse data for retrieving key parameters. Typically, we extracted HG parameters, such as \u003cem\u003eη\u003c/em\u003e of 10%, from an ohmic contacted ZnO/CQD p-i-n photodiode with identical geometrical dimensions and structures (Fig. S7). The inherent gain (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:G\\)\u003c/span\u003e\u003c/span\u003e) of the HGFET can be expressed as follows:\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:G=Rhv/q\\eta\\:\\)\u003c/span\u003e \u003c/span\u003e (3),\u003c/p\u003e \u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:R=\\frac{{I}_{ph}}{A{P}_{light}}\\)\u003c/span\u003e\u003c/span\u003e is the photoresponsivity. Considering an \u003cem\u003eR\u003c/em\u003e of up to 1.6\u0026times;10\u003csup\u003e5\u003c/sup\u003e A/W with a \u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003eds\u003c/em\u003e\u003c/sub\u003e bias of -0.1 V under 1300 nm irradiation at \u003cem\u003eP\u003c/em\u003e\u003csub\u003elight\u003c/sub\u003e of 0.46 nW/cm\u003csup\u003e2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec), the corresponding \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:G\\)\u003c/span\u003e\u003c/span\u003e is calculated to be ~\u0026thinsp;1.5\u0026times;10\u003csup\u003e6\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe response time of the HGFET detector is strongly dependent on the \u003cem\u003eV\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e applied to the CNT FET, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed, which demonstrates that increasing \u003cem\u003eV\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e from \u0026minus;\u0026thinsp;0.1 to -5 V results in a continuous decrease in the rise and decay times. The lowest rise time t\u003csub\u003eRise\u003c/sub\u003e (95 \u0026micro;s) and fall time t\u003csub\u003eFall\u003c/sub\u003e (415 \u0026micro;s) are achieved with a \u003cem\u003eV\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e bias of -5 V. According to the full photoelectric process of the HGFET shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed, the response time is dominated by two main processes, namely, the drift of photocarriers in the p-i-n heterojunction and the propagation delay in the CNT channel. The drift of photocarriers in the p-i-n heterojunction will occur at sub-microseconds, comparable to that of reported photodiodes with similar dimensions\u003csup\u003e28\u003c/sup\u003e, and CNT network FETs with a channel length of 10 \u0026micro;m typically exhibit a propagation delay of ~\u0026thinsp;100 \u0026micro;s\u003csup\u003e31\u003c/sup\u003e. Therefore, the speed of the detector is mainly constrained by carrier transport in long-channel CNT FETs. The photocurrent decay is much slower than the photocurrent rise because the detrapping process of charged trap states is slower than the trapping process\u003csup\u003e32, 33\u003c/sup\u003e. To enable high-speed detection, the photocurrent rise and fall time should be further reduced through other strategies, such as adopting aligned CNTs, reducing the channel length, and applying an electric pulse at the gate to facilitate the escape of trapped carriers\u003csup\u003e12\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe current noise spectrum of the HGFET detector (see detailed measurements in the Supplementary Information and Fig. S8a) shows a typical 1/\u003cem\u003ef\u003c/em\u003e frequency-dependent character, indicating that the total current noise is mainly contributed by the flicker noise. As evidence, the calculated lines of shot noise and thermal noise (Supplementary Sections 5 and 8) are far below the measured curve of the noise spectrum, while the simulated flicker noise is almost consistent with the measured noise curve. Considering the opto-electronic decoupling mechanism of HGFETs, electric noise can be categorized into two sources: noise originating from the heterojunction and noise stemming from the underlying CNT FET (the developed noise model is detailed in Supplementary Section 8). In the open-circuit state, only the preexisting thermal noise (\u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003enT\u0026minus;HG\u003c/em\u003e\u003c/sub\u003e) of the heterojunction can be amplified by \u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e and then coupled to the detector. Compared to the flicker noise of the CNT FET, this noise is negligible (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee), which was determined by comparing the current noise of the device before and after depositing the p-i-n heterojunction on the high-κ layer of the CNT channel (Fig. S11). Based on the measured photoresponsivity \u003cem\u003eR\u003c/em\u003e and electrical noise spectrum, the room-temperature specific detectivity (\u003cem\u003eD\u003c/em\u003e*) of the HGFET detector is plotted as a function of \u003cem\u003eP\u003c/em\u003e\u003csub\u003elight\u003c/sub\u003e at 1300 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee). \u003cem\u003eD\u003c/em\u003e* increases with decreasing \u003cem\u003eP\u003c/em\u003e\u003csub\u003elight\u003c/sub\u003e, and the peak value exceeds 10\u003csup\u003e14\u003c/sup\u003e Jones under weak light, which is recorded in all reported SWIR detections with measured noise data\u003csup\u003e3, 12, 13, 28\u003c/sup\u003e.\u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eGate-tuneable operating mode of the HGFET\u003c/h2\u003e \u003cp\u003eThe gain of the FET relies on the gate voltage, which will provide a factor to tune the detectivity of the HGFET detector. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea displays the transfer curves of an HGFET under an infrared radiation power density ranging from 0 to 1.08 \u0026micro;W/cm\u0026sup2; at 1300 nm. The threshold voltage (\u003cem\u003eV\u003c/em\u003e\u003csub\u003eth\u003c/sub\u003e) shifts by approximately 0.16 V due to the photovoltage-gated response. The photocurrent for the HGFETs has a positive power function dependent on the light intensity (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb) when gated in the subthreshold region (\u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e =-0.05 to -0.15 V) but exhibits a logarithmic function (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec) when gated in the linear region (\u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e =-1.2 to -1.3 V). Further analysis (Figs. S9 and S10) was conducted to determine the \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e-dependent responsivity and gain (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). Both the responsivity and gain increase with a power-law dependence on \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e in the subthreshold region and reach saturation at a \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e of approximately 0.5 V (see the fitted gain detailed in Supplementary Section 7); this is because the values are directly proportional to transconductance \u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e, which increases with \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e until the device enters the linear region. When operating in the linear region (\u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e ranging from \u0026minus;\u0026thinsp;1 to -2 V), a high inherent gain (~\u0026thinsp;10\u003csup\u003e7\u003c/sup\u003e) is achieved to amplify the photovoltage at the heterojunction of the HGFET in situ and provide a higher output current.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe measured current noise of the HGFET is also dependent on \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e, which exhibits characteristics similar like the transfer characteristics of a CNT FET (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee). The relation between \u003cem\u003eD\u003c/em\u003e* and \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e was extracted by combining the \u003cem\u003eR\u003c/em\u003e-\u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e curve in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed and the noise-\u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e curve in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef; these results demonstrate that the \u003cem\u003eD\u003c/em\u003e* of the HGFET strongly depends on the gate voltage with a similar behaviour to that of the simulation results (see details in Supplementary Section 9 and Fig. S12). Corresponding to the operating region of the FET tuned by \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e, the HGFET can operate in two typical modes, \u003cem\u003ei.e.\u003c/em\u003e, high-gain mode (in the linear region) and high-detectivity mode (in the subthreshold region). In high-gain mode, the HGFET detector can provide a high output current, which is beneficial for simplifying the readout circuit design. In high detectivity mode, the HGFET detector can provide high sensitivity for weak light detection with low power dissipation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003ePerformance comparison and benchmarking\u003c/h2\u003e \u003cp\u003eWe compared the performance of the HGFET detector and a commercial InGaAs photodiode (FGA015)\u003csup\u003e34\u003c/sup\u003e by directly testing the SWIR response characteristics under the same testing conditions (see details in Supplementary Section 10). Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea illustrates the detailed measurement system, enabling precise photoelectric testing and laser beam analysis. The output beam spot can be adjusted using two different objective lenses with amplification factors of 10\u0026times; and 50\u0026times; to match the optical areas of the two devices. The output power was modulated using adjustable slots and neutral density filters, and it was meticulously calibrated using a germanium power metre and a standard InGaAs photodiode (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). The time-resolved photoresponses under weak infrared irradiation at 1300 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb) show that the HGFET demonstrates a high SNR (\u003cem\u003eI\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e/\u003cem\u003eI\u003c/em\u003e\u003csub\u003en\u003c/sub\u003e) (approximately 70) at a light intensity as low as 0.46 nW/cm\u003csup\u003e2\u003c/sup\u003e, at which the InGaAs photodiode exhibits no response. As the InGaAs photodiode begins to show a weak current response (with an SNR of approximately 7), the light intensity increases to 3.78 nW/cm\u003csup\u003e2\u003c/sup\u003e. The photocurrent in the HGFET device (in the subthreshold region) exhibited a clear power-law relationship with the incident light intensity (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec), even when the power intensity was below 1 nW/cm\u003csup\u003e2\u003c/sup\u003e. However, the photocurrent in the InGaAs photodiode exhibits a linear relation with the light intensity and begins to deviate from the linear relation as the light intensity decreases below 100 nW/cm\u003csup\u003e2\u003c/sup\u003e; these results indicate that the responsivity is uncertain under weak light, mainly owing to the absence of inherent gain-induced low \u003cem\u003eR\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo preliminarily demonstrate the array ability of the HGFET detectors for passive night vision imaging, we fabricated an image sensor featuring 64\u0026times;64 pixels of HGFETs, and the pixel array was connected to the readout circuits on the printed circuit board (PCB, see details in Supplementary Section 11). Without an image lens, we displayed the \u0026ldquo;PKU\u0026rdquo; images acquired at different irradiation power densities using an assembled test system (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee). Despite far from optimizing device structure (lack of a gate switch transistor for each pixel and non-ideal electrical cross-talk within each row of the 64 pixels), the HGFET imager successfully captured the \u0026ldquo;PKU\u0026rdquo; pattern (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef) at a low power density (100 nW/cm\u0026sup2;), demonstrating the potential of HGFET for high sensitivity.\u003c/p\u003e \u003cp\u003eWe performed benchmarking tests for our HGFET detector using commercial photodiodes and other thin-film-based infrared photodetectors, focusing on important metrics such as specific detectivity and speed. In Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea, the wavelength-dependent \u003cem\u003eD\u003c/em\u003e* characteristics of our HGFET device are compared with those of InGaAs photodiodes (from Thorlabs and Hamamatsu) and Ge photodiodes (from Thorlabs) measured under identical setup and conditions. The HGFET achieved a peak \u003cem\u003eD\u003c/em\u003e* that exceeded 10\u003csup\u003e14\u003c/sup\u003e Jones, which is nearly two orders of magnitude greater than that of InGaAs photodiodes. This is the highest reported peak \u003cem\u003eD\u003c/em\u003e* for thin-film-based photodetectors in the SWIR range, facilitating detection under moonlight and even starlight conditions, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb and detailed in Table S2\u003csup\u003e34, 35\u003c/sup\u003e. Moreover, the sensitivity of HGFETs can be substantially improved by optimizing the \u003cem\u003eEQE\u003c/em\u003e of the CQD heterojunction and enhancing the gate efficiency of the FET; thus, it is possible to approach the fundamental limits defined by the signal fluctuation limit (SFL) and background limited infrared photodetection (BLIP) of approximately 10\u003csup\u003e18\u003c/sup\u003e Jones at 1300 nm\u003csup\u003e5\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSimilar to all reported electrical devices with internal gain\u003csup\u003e17\u003c/sup\u003e, a trade-off occurs between the gain (\u003cem\u003eG\u003c/em\u003e) and bandwidth in photodetectors, including the HGFET, and the gain-bandwidth (\u003cem\u003eGBW\u003c/em\u003e) product is the key metric for characterizing the comprehensive performance in terms of the sensitivity and speed of a photodetector with gain. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec presents the \u003cem\u003eGBWs\u003c/em\u003e of five typical detectors with different architectures, including photoconductors\u003csup\u003e36\u003c/sup\u003e, photodiodes\u003csup\u003e18, 34\u003c/sup\u003e, APDs\u003csup\u003e26, 27\u003c/sup\u003e, photogating devices\u003csup\u003e12\u003c/sup\u003e, and HGFETs. A maximum \u003cem\u003eGBW\u003c/em\u003e of 15.5 GHz was achieved in the HGFET with randomly oriented CNT films, which outperforms all reported thin-film-based infrared detectors and InGaAs PIN diodes\u003csup\u003e13, 18, 25, 28\u003c/sup\u003e (Fig. S20). With the much higher carrier mobility than randomly oriented CNT film, aligned semiconducting CNT films have been considered as a superior semiconducting channel in constructing FETs with high \u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e and speed\u003csup\u003e38\u003c/sup\u003e. Thus, the HGFET based on aligned CNTs exhibits a \u003cem\u003eGBW\u003c/em\u003e of up to 69.2 THz alongside a \u003cem\u003eD\u003c/em\u003e* of 6.7\u0026times;10\u003csup\u003e13\u003c/sup\u003e Jones (Figs. S20 and S21) and far exceeds that of all existing infrared detectors, including the latest advanced APD devices\u003csup\u003e13, 26, 27\u003c/sup\u003e. This outstanding \u003cem\u003eGBW\u003c/em\u003e performance of the HGFET primarily results from the physical mechanism of opto-electric decoupling, specifically rapid photocarrier separation facilitated by the built-in potential, ultrafast electrostatic coupling, swift charge transport within the CNT channel, and excellent signal amplification capability of the CNT FET.\u003c/p\u003e \u003cp\u003eOpto-electrical decoupling enables HGFETs provide greater controllability and can help alleviate trade-offs between photon absorption and electrical noise, as well as between gain and response speed. Excellent optical and electrical properties can be achieved simultaneously in one device by employing two solution-processed semiconductors rather than relying on single-crystalline materials that necessitate precise lattice matching; this process may promote the monolithic integration of HGFET detector arrays with silicon ROICs through a back end of line (BEOL)-compatible process. Furthermore, HGFETs can replace the light absorber and serve as a versatile platform for photodetection across various wavelength bands; thus, the detector can be adapted to different optical applications.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eWe have reported an opto-electric decoupling HGFET SWIR detector that presents a high inherent gain for amplifying signals while barely amplifying noise for detecting weak infrared radiation. The HGFET devices exhibit a recorded detectivity of 1.27\u0026times;10\u003csup\u003e14\u003c/sup\u003e Jones and a maximum gain-bandwidth product of 69.2 THz to 1300 nm irradiation at room temperature. The opto-electric decoupling device can detect weak infrared radiation of 0.46 nW/cm\u003csup\u003e2\u003c/sup\u003e, which is much more sensitive than the commercial and all reported SWIR detectors and especially enables a starlight detection or vision. As the fabrication process of HGFET is highly compatible with CMOS readout integrated circuits, the HGFET offers a universal platform for achieving high-end passive night vision image sensors in thin-film semiconductors; this technology paves the way for innovative optoelectronic circuits and future monolithically integrated systems with high resolution, high sensitivity and low cost.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eMaterials preparation\u003c/h2\u003e \u003cp\u003ePolymer-sorted, solution-derived CNTs with a semiconductor purity exceeding 99.999% were prepared using dispersion and centrifugation, as detailed previously in the literature\u003csup\u003e37\u003c/sup\u003e. The polymer-wrapped CNT solution was then diluted with toluene. Randomly oriented CNT films with high uniformity were formed by immersing the cleaned substrate in a diluted CNT solution for 48 hours. A dimension-limited self-alignment (DLSA) procedure was employed to deposit aligned CNT films, as previously described in the literature\u003csup\u003e38\u003c/sup\u003e. Next, a cleaning process involving coating with yttrium oxide (Y\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) and then decoating to remove the polymer was carried out. Finally, thermal annealing was conducted at 600\u0026deg;C in an Ar/H\u003csub\u003e2\u003c/sub\u003e atmosphere.\u003c/p\u003e \u003cp\u003eThe synthesis of PbS CQDs with oleylamine ligands was executed following a solution-processed procedure detailed in prior studies\u003csup\u003e28, 29\u003c/sup\u003e. In the ambient atmosphere, a solution-phase ligand exchange process was conducted to synthesize PbS-halide CQDs. These CQDs were then dispersed in a mixture of amylamine, hexylamine, and butylamine (in a volume ratio of 3:2:10) at a concentration of 150 mg/mL to prepare the PbS-halide CQD ink for film fabrication. The construction of the ZnO/PbS CQD heterojunction began with the sputtering of a 40 nm-thick ZnO thin film utilizing a previously described method\u003csup\u003e39\u003c/sup\u003e. Next, a 150 nm thick absorbing layer was deposited onto the ZnO thin film via spin coating the PbS-halide CQD ink at 2500 rpm for 20 seconds. The final step involved depositing two layers of PbS CQDs treated with 1,2-ethanedithiol (EDT, 0.02 vol% in an acetonitrile solution) to serve as the p-doped layer. The doping concentrations of the prepared ZnO film and PbS-EDT CQDs were previously measured to be ~\u0026thinsp;10\u003csup\u003e17\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eHGFET fabrication\u003c/h2\u003e \u003cp\u003eThe HGFET detectors were constructed on Si/SiO\u003csub\u003e2\u003c/sub\u003e substrates. As illustrated in Fig. S2, the local bottom-gate metal was patterned using photolithography and electron beam evaporation (EBE) of a Ti/Pd film (1/20 nm) via a standard lift-off process. A 10 nm thick (100 cycles) layer of hafnium oxide (HfO\u003csub\u003e2\u003c/sub\u003e) dielectric was deposited onto the gate metal using atomic layer deposition. Subsequently, a CNT film was deposited onto the HfO\u003csub\u003e2\u003c/sub\u003e dielectric and patterned through photolithography and reactive ion etching (RIE) to create the channel region. Source (\u003cem\u003eS\u003c/em\u003e) and drain (\u003cem\u003eD\u003c/em\u003e) pads were then created through photolithography, EBE of a Ti/Pd/Au film (0.3/40/30 nm), followed by a standard lift-off process. An ultrathin Y\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e layer (~\u0026thinsp;6 nm) was deposited on the CNT channel through thermal oxidation at 270 ℃ in air, serving as the dielectric for the floating gate. Finally, the p-i-n heterojunction was constructed by sequentially depositing the ZnO film, PbS-halide CQD film, and PbS-EDT CQD film.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eHGFET imager fabrication\u003c/h2\u003e \u003cp\u003eThe fabrication process, as illustrated in Fig. S15, began with the deposition of a randomly oriented CNT film on a 4-inch Si/SiO\u003csub\u003e2\u003c/sub\u003e substrate, followed by patterning using photolithography and RIE. Next, the source/drain electrodes and the lower interconnect line were patterned by photolithography, followed by EBE of a 30 nm Pd film and subsequent lift-off processing. An isolation layer of 60 nm SiO\u003csub\u003e2\u003c/sub\u003e was deposited using photolithography, EBE, and a subsequent lift-off process. The upper interconnect line was then formed by photolithography and deposition of a 20/600 nm Ti/Au film via EBE. Following this procedure, similar steps were performed to deposit the ultrathin Y\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e layer and p-i-n heterojunction. Finally, an HGFET array with 64\u0026times;64 pixels was constructed and wire bonded to the readout circuit board.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eCharacterization of the materials and device\u003c/h2\u003e \u003cp\u003eSEM images were obtained using a FEI ZEISS Sigma 300 scanning electron microscope. The optical absorption spectra of the PbS CQDs were measured with a UV-3600 plus spectrophotometer. The Raman spectrum of the CNT film was collected by a LabRAM HR800 instrument (Jobin-Yvonr). Optoelectronic measurements of the HGFET devices and the InGaAs diode were conducted using the measurement system depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea. A supercontinuous spectrum laser from the NKT Company was utilized to characterize the device responses, with the laser wavelength adjustable from 640 to 2100 nm. The spectral responsivity of the devices was assessed using a monochromator and calibrated against a standard InGaAs diode (FGA21, Thorlabs). Photocurrent spectroscopy was performed using an SR830 lock-in amplifier in conjunction with an SR540 chopper and a tungsten lamp equipped with monochromator, all of which were controlled by a LabVIEW program. The transient response and \u0026minus;\u0026thinsp;3 dB bandwidth were measured using a high-speed oscilloscope (Agilent DSO7054A). Current noise spectra were obtained using the PDA FS380 (Bodawei Electronic Technology Co., Ltd.) and E4727B (Keysight Technologies Co., Ltd.) systems. All electronic transport measurements were carried out using a Keithley 4200 semiconductor analyser at room temperature under ambient conditions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eImage capture\u003c/h2\u003e \u003cp\u003eA schematic diagram of the assembled test system is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee. The setup involves collimated infrared light emitted from a 940 nm LED source (M940L3-C4 from Thorlabs) with a beam diameter of 44 mm. The power density of the light was modulated using neutral density filters. A photomask containing the designed patterns was used to provide a spatial light distribution, which was subsequently captured by the 64\u0026times;64 pixel HGFET imager.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eDetector characteristics\u003c/h2\u003e \u003cp\u003eThe calculated gain of the HGFET, as outlined in Section 2 (Supporting Information), is directly linked to the transconductance (\u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e). The calculated photocurrent, which was described in Section 4, exhibits a positive power function in the subthreshold region of the CNT FET and a logarithmic function in the linear region. These distinctive response characteristics were further validated by comparing the extracted \u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e and subthreshold swing (\u003cem\u003eSS\u003c/em\u003e) of HGFETs with those of top metal-gated CNT FETs. TCAD simulations were constructed and illustrated a continuously fitted photocurrent under various irradiation conditions (refer to Fig. S7). The specific parameters used for the TCAD simulation are detailed in Section 4. The noise characteristics are described in Section 8, and the calculated expressions for the HGFET noise are provided. The detectivity characteristics of HGFETs are presented in Section 9, illustrating how the signal-to-noise ratio (SNR) is proportional to \u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e/\u003cem\u003eI\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e in the subthreshold region and \u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e/\u003cem\u003eI\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e in the linear region.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability. \u003c/strong\u003eThe data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work is supported by the Natural Science Foundation of China (62225101 and U21A6004) and the Peking Nanofab Laboratory.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eZ.Z. and Y.W. advised on and led this project. S. Z. carried out the device fabrication and experimental measurements. X. Z. carried out the aligned CNT-based HGFET fabrication and measurements. S.Z. and P.Z. provided the TCAD simulation. D.L. and J.J. designed and provided the readout circuit boards. L. X. and D. Z. synthesized the PbS CQDs and fabricated the CQDs photodiodes. S.Z., Y.W., and Z.Z. wrote the paper. All authors discussed the results and prepared and commented on the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe supplementary material is contained.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003e1. Xia F., Wang H., Di Xiao, Dubey M. \u0026amp; Ramasubramaniam A. Two-dimensional material nanophotonics. \u003cem\u003eNat. 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Highly sensitive SWIR photodetector using carbon nanotube thin film transistor gated by quantum dots heterojunction. \u003cem\u003eAppl. Phys. Lett.\u003c/em\u003e \u003cb\u003e120\u003c/b\u003e, 193103 (2022).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"infrared photodetector, carbon nanotubes, weak infrared radiation detection, opto-electric decoupling, sensitivity","lastPublishedDoi":"10.21203/rs.3.rs-4705743/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4705743/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHighly sensitive shortwave infrared (SWIR) detectors are essential for detecting weak radiation (typically below 10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e W\u0026middot;Sr\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u0026middot;\u0026micro;m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) with high-end passive image sensors. However, mainstream SWIR detection technology is based on epitaxial photodiodes, which cannot effectively detect ultraweak infrared radiation due to the lack of inherent gain. Here, we developed a heterojunction-gated field-effect transistor (HGFET) consisting of a colloidal quantum dot (CQD)-based p-i-n heterojunction and a carbon nanotube (CNT) field-effect transistor, which achieves a high inherent gain based on an opto-electric decoupling mechanism for suppressing noise. The stacked heterojunction absorbs infrared radiation and separates electron-hole pairs. Then, the generated photovoltage tunes the drain current of the CNT FET through an Y\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e gate insulator. As a result, the HGFET significantly detects and amplifies SWIR signals with a high inherent gain while minimally amplifying noise, leading to a recorded specific detectivity above 10\u003csup\u003e14\u003c/sup\u003e Jones at 1300 nm and a recorded maximum gain-bandwidth product of 69.2 THz. Direct comparative testing indicated that the HGFET can detect weak infrared radiation at 0.46 nW/cm\u003csup\u003e2\u003c/sup\u003e levels; thus, compared to commercial and reported SWIR detectors, this detector is much more sensitive and enables starlight detection or vision. As the fabrication process is very compatible with CMOS readout integrated circuits, the HGFET is a promising SWIR detector for realizing passive night vision imaging sensors with high resolutions that are high-end, highly sensitive, and inexpensive.\u003c/p\u003e","manuscriptTitle":"Opto-electrical decoupled phototransistor for starlight detection","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-08-05 20:15:07","doi":"10.21203/rs.3.rs-4705743/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"6369313e-1a37-42c6-b363-63d07ffe4c50","owner":[],"postedDate":"August 5th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":35115403,"name":"Physical sciences/Engineering/Electrical and electronic engineering"},{"id":35115404,"name":"Physical sciences/Nanoscience and technology/Nanoscale devices/Electronic devices"}],"tags":[],"updatedAt":"2024-08-05T20:15:07+00:00","versionOfRecord":[],"versionCreatedAt":"2024-08-05 20:15:07","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4705743","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4705743","identity":"rs-4705743","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}