Analysis of optical and thermal properties of 940-nm vertical-cavity surface-emitting lasers

Analysis of optical and thermal properties of 940-nm vertical-cavity surface-emitting lasers | 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 Research Article Analysis of optical and thermal properties of 940-nm vertical-cavity surface-emitting lasers Congcong Wang, Chong Li, Zhiyong Wang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-1278067/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract We achieve 13.5mW optical output power, 48% power conversion efficiency, 1.17 W/A slope efficiency and 17kW/cm 2 laser power density with top-surface-emitting 940 nm oxide-confined vertical-cavity surface-emitting laser (VCSEL). The physical mechanism of minimum threshold current generation in oxide-confined VCSEL has been thoroughly studied theoretically and experimentally. Further, we also succeeded in 90.8mW optical output power, 40% power conversion efficiency with 2×4 VCSEL arrays. We find an increase in output power and PCE of 2×2 VCSEL arrays as we increase the array spacing which we attribute primarily to increased heat dissipation and reduced thermal crosstalk between the emitters. Thermal properties in oxide-confined 2×2 VCSEL arrays were analyzed numerically and experimentally. The simulated results are in good agreement with the measurement. It is proved that theoretical simulation is very useful for the future device optimization. VCSEL arrays the minimum threshold current power thermal properties Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction Vertical-cavity surface-emitting lasers (VCSELs) have advantages of symmetrical laser beam, low threshold, high-speed modulation, single longitudinal mode, lack of catastrophic optical mirror damage (COMD), and simple arrangement in two dimensional arrays(Chuyu et al. 2017 ; Lu et al. 2015 ; Seurin et al. 2010 ; Larisch et al. 2016 ; Seurin et al. 2016; Tatsuo Hariyama et al. 2018 ). They have been used in optical interconnect, high-speed local-area networks parallel links, Gigabit Ethernet, atomic clock system, free-space data transmission, laser pumping and illumination field. Moreover, 940-nm VCSELs have been innovatively applied in the fields of three-dimensional (3D) face recognition, laser radar, automobile auxiliary driving, artificial intelligence robot and virtual reality/augmented reality (VR/AR) (Tatsuo Hariyama et al. 2018 ; Yong-Qin et al. 2011 ; Shichijo,Miyamoto 2019 ; Nazaruk et al. 2014 ). In laser pumping, laser radar, 3D sensing, illumination and other highly integrated fields need VCSEL with high output power and photoelectric conversion efficiency (PCE). In some extreme temperature conditions, temperature changes will seriously affect the performance of VCSELs. Extensive application in optical fiber sensing and core chip atomic clock system, require VCSELs with low threshold, wavelength stability and low temperature sensitivity(Derebezov et al. 2010 ; Nishikata et al. 2005 ; HuiQing et al. 2004 ; Tong 2005 ). Some scholars have studied the output power, PCE, beam quality and working stability of VCSEL. Moench H et al. reported the 808-nm VCSEL array combination with the photoelectric conversion efficiency (PCE) of up to 40% and output power of 9.6kW(Moench et al. 2014a; Moench et al. 2014b ). Zhou D. L. et al investigated the 980-nm VCSEL array combination with photoelectric conversion efficiency of up to 40% and output power of 14kW(Zhou et al. 2015b; Zhou et al. 2014). Osram power of 1W(Iga,Kenichi 2018). Meng Xun et al. studied the 940-nm VCSEL array with output developed the 940-nm VCSEL array with electro-optic conversion efficiency of up to 35% and output power of 210mW(Meng Xun et al. 2021 ). Compared with the 808-nm and 980-nm VCSEL array, the performance of 940-nm VCSEL array is relatively poor. The internal thermal and thermal crosstalk effect of the VCSEL array is one of the most significant factors, which affect the output power and PCE. A high temperature will reduce the output characteristics and lifetime of VCSEL array. Heat sources of VCSEL consist of two parts: joule heating of DBR (especially P-DBRs) and heating of the active region. Compared with 808-nm VCSEL array, 940-nm VCSEL array produces more heat due to more P-distributed Bragg reflectors (DBRs). What is more serious is that top-emitted 940-nm VCSEL array has poor cooling effect compared with the bottom-emitted 980-nm VCSEL array. In this paper, our main attention will be focused on the photoelectric properties of 940-nm VCSEL and its arrays. Firstly, temperature dependence of threshold current, the output power and electro-optic conversion efficiency (PCE) of VCSEL were studied, and the mechanism of the minimum threshold current was analyzed in detail. Then, the output power and PCE of 2×2 VCSEL arrays with different arrays spacing (d=160µm, 180µm and 200µm) were systematically analyzed. In addition, 3D thermoelectric coupling models were established based on finite element analysis to investigate the thermal distribution of 2×2 VCSEL arrays. 2. Fabrication The GaAs-based 940nm VCSEL epitaxial structure consists of 23 pairs Al 0.12 Ga 0.88 As/Al 0.9 Ga 0.1 As layers for the P-DBRs and 32 pairs Al 0.12 Ga 0.88 As/AlAs layers for the N-DBRs. The active region includes three strained 4.4-nm-thick In 0.16 Ga 0.84 As quantum wells (QWs) and four 6.2-nm-thick strain-compensating GaAs 0.92 P 0.08 barriers. The QWs with high In-content for wavelength extension and strain compensating GaAs 0.92 P 0.08 barriers for compressive strain in the QWs for high differential gain(Simpanen et al. 2019 ). Carriers and photons are well-confined along the transverse direction by a 30nm thick Al 0.98 Ga 0.02 As oxide aperture on the P-DBRs. The top-emitted 940-nm VCSEL array chip fabrication is as follows. First, etched circular top mesas just through the optical cavity with Cl 2 + BCl 3 in an inductively coupled plasma (ICP) reactive ion etching to expose high Al content layer. Then oxide aperture (Φ = 10 µm) was formed by the selective wet oxidation of Al 0.98 Ga 0.02 As to Al 2 O 3 at temperature of 430℃. Ti/Au mental contact was deposited on the top of wafer by using electron beam evaporation system. SiN layer was deposited to form an insulating layer. After the GaAs substrate was thinned to 150µm, the Ni/Au/Ge/Ni/Au mental contact was deposited on the bottom of wafer by using measurement and control sputtering system. Finally, the contacts were rapidly annealed at 435 ℃. Figure. 1 shows the sectional diagram of VCSEL array. 3. Results And Discussion The VCSEL arrays were tested on a probe station using a semiconductor parameter analyzer (Keithley 4200), a high precision current source (Keithley 2430), a laser beam profiler (Spiricon SP928), a power meter (Thorlabs S120C) and a spectrograph (Yokogawa AQ6370D). A thermo electric cooler (TEC) can control the temperature vary from -30℃ to 40℃. Figure. 2 shows schematics of experiment setup in our experiment. All the performance parameters of VCSELs are obtained by on-chip test under continuous wave condition without extra heat dissipation solution. Figure 3 (a) showed the temperature-dependent threshold currents (I th ) and slope efficiency for top-emitting VCSEL. And the relationship of threshold currents and temperature meets the parabolic equation (1). Under the same condition of injection current, operating temperature affects the threshold current and slope efficiency. As the operating temperature rises, the internal temperature of the device increases, which results in a reduction in output power and power conversion efficiency (PCE). As is shown in the figure. 3(a), the threshold current decreases at first and then increases as the temperature increases in the case-temperature range from -30 ℃ to 40℃. The minimum threshold currents (I th, min ) of 10-µm oxide aperture VCSEL was 0.995mA, when the environment temperature was 20℃. $${I}_{th}\left(T\right)={I}_{th},\text{m}\text{i}\text{n}\times \left[1+{C}_{T}{\left(T-{T}_{min}\right)}^{2}\right] \left(1\right)$$ where C T is a constant, C T =9.16×10 −5 ; T min is the temperature of the minimum threshold current, T min =19.3℃; I th, min is the minimum threshold current, I th, min =1mA; I th (T) is the threshold current in different temperature (T). The mode wavelength (MW) and gain peak wavelength (GPW) of VCSEL are two main factors that affect the threshold current of VCSEL. In order to study the physical mechanism of VCSEL threshold current generation, the reflection spectrum of DBR (contains P-DBR and N-DBR) and gain spectrum of active region were simulated using TFCalc and Crosslight software under the operating temperature of -30℃ ཞ 40℃. The reflectivity spectrums were calculated by transfer matrix method. Among them, the minimum point in the reflection spectrum corresponds to the resonance condition, so the mode wavelength can be obtained from the reflection spectrum of VCSEL(Wang et al. 1995 ). Figure. 3(b) showed the mode wavelength (MW) and gain peak wavelength (GPW) of the 10µm VCSEL (10mA) under the operating temperature of -30℃ ཞ 40℃. With the increase of temperature, the mode wavelength and gain peak wavelength of VCSEL were redshift. The redshift rate of mode wavelength is 0.0557 nm/℃. As is known, the mode wavelength of a VCSEL is determined by the cavity resonance due to the short optical resonator. The wavelength shift mainly depends on changes of the average refractive index in the resonator(Michalzik 2013 ). The redshift rate of gain peak wavelength is 0.33 nm/℃. As the temperature increases, the crystal lattice constant increases. This leads to a weakening of the binding effect of the valence electron period potential. The energy required for the valence electron transition decreases and the band gap shrinks. Bandgap shrinkage causes gain peak wavelength redshift. The peak gain decreases as the temperature increases, due to electron occupancy probability near the Fermi level is smoothness. A minimum threshold current of a VCSEL value exists, when the gain wavelength is the same as the mode wavelength at a temperature of 20°C, due to temperature-dependent gain and mode wavelength shifts. The physical mechanism of VCSEL threshold current generation was verified by combining theory and experiment. Figure. 4 showed the measured (a) temperature-dependent power, current, voltage (P-I-V) and (b) PCE characteristics of 10µm VCSEL. As is shown in figure. 4(a), the maximum output power is 13.5mW at -30°C and decreases to 9.6mW at 40°C. The slope efficiency is 1.17 W/A at -30°C and decreases to 0.98 W/A at 40°C. With the temperature increases, electron hole non-radiative recombination especially auger recombination is strengthened. More electric energy is released in the form of phonons, internal losses increasing with the temperature, which leads to a decrease of the differential efficiency and output power. Lower carrier concentration and higher carrier mobility can reduce the differential resistance. With the increase of temperature, the carrier concentration in the active region increases, and the probability of collision between carriers and ionized impurities increases, which leads to the decrease of carrier mobility. Temperature-dependent I-V curve means that the differential resistance of VCSEL was decreased with temperature increasing. This result indicates that the main factor determining differential resistance of VCSEL is the carrier concentration in the active region, and the secondary factor is the carrier mobility. As is shown in figure. 4(b), when the injection current is about 5mA, the PCE reaches the maximum value. Among them, the highest efficiency can reach 48% at 20°C. When the injection current is about 13.5mA, laser power density is up to 17kW/cm 2 at -30°C. To examine the beam property, the far-field patterns of the VCSEL at 20°C were measured at a distance of 50 mm from the VCSEL surface by a laser beam profiler. The far-field beam profile is symmetric and the intensity is near uniform, the far-field divergence angle is 23° at 13.5 mA. Through the above experiments, we found that 10-µm oxide aperture VCSEL has higher electro-optical conversion efficiency and power density, but overall output power was low. In order to improve the output power of VCSELs, the photoelectric performances of 2×2 and 2×4 VCSEL arrays with oxidation aperture of 10µm were studied systematically. Figure. 5 shows the output power and PCE of 2×2 VCSEL arrays. As the VCSEL array spacing (d) is 200µm, the maximum PCE was 47.2% at -30 ℃ and decreased to 40.06% at 40 ℃; the maximum power was 48.72mW at -30 ℃ and decreased to 32.93% at 40 ℃. Full width half maximum (FWHM) was 1.05nm at -30 ℃ and decreased to 1.42nm at 40 ℃, respectively. The spectral broadening rate is only 0.0053nm/℃. The beam distribution is relatively uniform, and the divergence angle is about 20°. With increasing temperature and the decrease of the array spacing, the output power and PCE show a downward trend. The main cause of this phenomenon is heat accumulation caused by thermal resistance effect. In addition, in order to increase the power of the VCSEL array, the 2×4 VCSEL array (d=200 µm) was prepared, and the maximum power and PCE were 90.8mW and 40% at -30 ℃, respectively. The spectral broadening rate is 0.007nm/K. The above measured data conform that device exhibited superior adaptability to high and low temperatures operation characteristics. In order to analyze the thermal effect of VCSEL, its thermal resistance of can be obtained from the emission spectra and dissipated power. The thermal resistance equation (2) is(Zhou et al. 2015a ) $${R}_{th}=\frac{\varDelta T}{\varDelta {P}_{diss}}=\frac{\varDelta \lambda /\varDelta {P}_{diss}}{\varDelta \lambda /\varDelta {T}_{a}} \left(2\right)$$ ∆P diss is the dissipated power. The dissipated power is equal to injected electrical power subtracting output optical power. ∆λ/∆P diss is calculated by variation of the wavelength shift with the variation of the dissipated power (Zhou et al. 2015a ). ∆λ is the wavelength shift rate, ∆T a is the varied ambient temperature. The thermal resistance was obtained by analyzing the experimental photoelectric performance parameters of 2×2 VCSEL array (d=200µm). Fig. 6 (a) shows the measured temperature-dependent emission wavelength, the wavelength shifts with ambient temperature linearly by a rate of 0.054 nm/℃. The relationship between peak wavelength and dissipated power is shown in Fig. 6 (b), which obtained by measuring the emission spectra under different injection currents at ambient temperature of 20 ℃. When the injection current was 40mA, ∆λ/∆P diss is 0.028 nm/mW. The dissipated power (P diss ) is 70mW. According to (2), the thermal resistance is 0.515 ℃/mW. The equation of actual temperature in active region (T ac ) is as follows: T ac =T a + R th P diss . In this case, the actual temperature in active region is 56.04 ℃. In order to analyze the thermal distribution of 2×2 VCSEL arrays (d=160µm, 180µm and 200µm), a 3D thermoelectric coupling model based on finite element analysis was established by COMSOL Multiphysics. In this model, the equivalent structure method is adopted to simulate the VCSEL structure, whose structure mainly includes: P-DBR, active region, N-DBR and GaAs substrate. Joule heat and heat generation in active region are two main sources of VCSEL heat generation. The resistance is generated by the VCSEL heterojunction barrier structure and the parasitic resistance of the VCSEL array, interact with the current to produce a large amount of joule heat. The carrier injection, carrier leakage, carrier recombination and absorption loss occurring in the active region will generate a large amount of heat, which becomes the main heat source of the active region. In this model, the ambient temperature is set to 20℃ and the injection current of each light source is set to 10mA. Figure. 7 shows the simulated temperature distributions and temperature curve along A-A’ cut-line in active region. As is shown in Fig. 7 , the maximum temperatures in active region were 63.1 ℃ @160µm, 59.1℃@180µm and 55.9℃@200µm, respectively. When the array spacing is 200µm, the simulation results are consistent with the actual results, which proves the correctness of the simulation results. According to the above experimental results, optimizing the thermal accumulation of devices can improve the output power and PCE. Therefore, in order to obtain high-power VCSEL, it is necessary to optimize the epitaxial structure, such as reasonably increasing doping concentration, designing gradual DBR structure and reduce the pairs of DBRs. The DBRs have gradient composition interfaces and are modulation doped for efficient transport of carriers across the interfaces and low internal optical loss(Simpanen et al. 2019 ). In order to improve the heat dissipation performance of the device, the device can use the 3D micro-channel heat sink of tungsten copper alloy with Pin Fin structure to conduct water cooling heat dissipation. 4. Conclusion And Perspectives In summary, the physical mechanism of minimum threshold current generation in oxide-confined VCSEL has been thoroughly studied theoretically and experimentally. That is, the threshold current reaches the minimum value when the mode wavelength matches the gain wavelength. VCSEL with an oxide aperture diameter φ∼10 µmexhibit 13.5 mW operating optical output power and 1.17 W/A slope efficiency at -30°C. And its highest PCE and laser power density are up to 48% at and 17kW/cm 2 . The 2×2 VCSEL array (d=200µm) exhibit the maximum PCE was 47.2% at -30 ℃ and decreased to 40.06% at 40 ℃; the maximum power was 48.72mW at -30 ℃ and decreased to 32.93% at 40 ℃. Full width half maximum (FWHM) was 1.05nm at -30 ℃ and increased to 1.42nm at 40 ℃, respectively. The spectral broadening rate is only 0.0053nm/℃. The 2×4 VCSEL array (d=200µm) exhibit the maximum power was 90.8 mW at -30 ℃. We find an increase in output power and PCE of 2×2 VCSEL array as we increase the array spacing which we attribute primarily to increased heat dissipation and reduced thermal crosstalk between the emitters. Thermal properties in oxide-confined 2×2 VCSEL arrays were analyzed numerically and experimentally. The simulated results agree well with the measurement. It is proved that theoretical simulation is very useful for the future device optimization. Declarations Acknowledgments This work was supported in part by the National Natural Science Foundation (61505003, 61674140) and Beijing education commission project (SQKM201610005008). References Chuyu, Z., Xing, Z., Di, L., Yongqiang, N., Lijun, W.: Enhanced thermal stability of VCSEL array by thermoelectric analysis-based optimization of mesas distribution. Chin. Phys. B 26 (06), 157–164 (2017) Derebezov, I.A., Haisler, V.A., Bakarov, A.K., Kalagin, A.K., Toropov, A.I., Kachanova, M.M., Gavrilova, T.A., Semenova, O.I., Tretyakov, D.B., Beterov, I.I., Entin, V.M., Ryabtsev, I.I.: Single-mode vertical-cavity surface emitting lasers for 87Rb-based chip-scale atomic clock. Semiconductors+ 44 (11), 1422–1426 (2010) HuiQing, L., Jie, Z., DaFu, C., ZuYan, X., YongQiang, N., ChangLing, Y., Li, Q., Yun, L., LiJun, W., JianLin, C.: Optimal designs for high-power vertical cavity surface emitting lasers. Acta Physica Sinica 53 (9), 2986–2990 (2004) Iga, K.: Forty years of vertical-cavity surface-emitting laser: Invention and innovation. Jpn. J. Appl. Phys. 57 (8), 08PA01 (2018) Larisch, G., Moser, P., Lott, J.A., Bimberg, D.: Impact of Photon Lifetime on the Temperature Stability of 50 Gb/s 980 nm VCSELs. Ieee Photonic Tech L 28 (21), 2327–2330 (2016) Lu, H.H., Li, C.Y., Chu, C.A., Lu, T.C., Chen, B.R., Wu, C.J., Lin, D.H.: 10 m/25 Gbps LiFi transmission system based on a two-stage injection-locked 680 nm VCSEL transmitter. Opt Lett 40 (19), 4563–4566 (2015) Meng Xun, G., Pan, Z., Zhao, Y., Sun, C., Yang, Kan, Q.: Analysis of Thermal Properties of 940-nm Vertical Cavity Surface Emitting Laser Arrays. IEEE TRANSACTIONS ON ELECTRON DEVICES 68 (1), 158–163 (2021) Michalzik, R.: VCSELs, vol. 166. Fundamentals, Technology and Applications of Vertical-Cavity Surface-Emitting Lasers. Springer-Verlag, Berlin Heidelberg (2013) Moench, H., Andreadaki, A., Gronenborn, S., Kolb, J.S., Loosen, P., Miller, M., Schwarz, T., van der Lee, A., Weichmann, U.: High power electrically pumped VECSELs and arrays. Paper presented at the Vertical External Cavity Surface Emitting Lasers (Vecsels) Iv, San Francisco, CA Moench, H., Kolb, J.S., Engelhardt, A.P., Gerlach, P., Witzigmann, B.: Optimized VCSELs for high-power arrays. Proceedings of SPIE 9001 (3), 395-406: (2014b) Nazaruk, D.E., Blokhin, S.A., Maleev, N.A., Bobrov, M.A., Kuzmenkov, A.G., Vasil'ev, A.P., Gladyshev, A.G., Pavlov, M.M., Blokhin, A.A., Kulagina, M.M., Vashanova, K.A., Zadiranov, Y.M., Fefelov, A.G., Ustinov, V.M.: Single-mode temperature and polarisation-stable high-speed 850nm vertical cavity surface emitting lasers. J Phys Conf Ser 572 , 012036 (2014). doi:Unsp 012036 1088/1742-6596/572/1/012036 Nishikata, K., Yokouchi, N., Koyama, F.: Wide temperature operation of 850-nm VCSEL and isolator-free operation of 1300-nm VCSEL for a variety of applications. Proceedings of SPIE - The International Society for Optical Engineering 5737 , 8-19: (2005) Seurin, J.-F., Zhou, D., Xu, G., Miglo, A., Li, D., Chen, T., Guo, B., Ghosh, C.: High-efficiency VCSEL arrays for illumination and sensing in consumer applications. Paper presented at the Conference on Vertical-Cavity Surface-Emitting Lasers XX, San Francisco, CA Seurin, J.F., Xu, G.Y., Wang, Q., Guo, B.M., Van Leeuwen, R., Miglo, A., Pradhan, P., Wynn, J.D., Khalfin, V., Ghosh, C.: High-brightness pump sources using 2D VCSEL arrays. Vertical-Cavity Surface-Emitting Lasers Xiv 7615 : (2010). doi:Artn 76150f 1117/12.842492 Shichijo, T., Miyamoto, T.: Rate equation-based numerical analysis of mutual injection for phase locked 2D-VCSEL array using Talbot effect. Jpn. J. Appl. Phys. 58 (1), SJJC01 (2019) Simpanen, E., Gustavsson, J.S., Larsson, A., Karlsson, M., Sorin, W.V., Mathai, S., Tan, M.R., Bickham, S.R.: 1060 nm Single-Mode VCSEL and Single-Mode Fiber Links for Long-Reach Optical Interconnects. J Lightwave Technol 37 (13), 2963–2969 (2019) Tatsuo Hariyama, P.A.M., Sandborn, M., Watanabe, Wu, M.C.: High-accuracy range-sensing system based on FMCW using low-cost VCSEL. Opt. Express 26 (7), 9285 (2018) Tong, C.Z.: Design and analysis of 1.3 µm GaAs-based quantum dot vertical-cavity surface-emitting lasers. Acta Physica Sinica 54 (8), 3651–3656 (2005) Wang, H., Xu, W., Cheng, Q., Ji, Z., Gao, R., Wu, P., Xu, Z.: Phase-Locking of a Gunn Oscillator at 3 mm Waveband Using High Temperature Superconducting Josephson Junction Harmonic Mixer. Chin. Phys. Lett. 12 (4), 253 (1995) Yong-Qin, H., Yan, L., Yuan, F., Chang-Ling, Y., Ying-Jie, Z., Yu-Xia, W., Xiao-Hua, W., Yi, Q., Guo-Jun, L.: Large aperture vertical cavity surface emitting laser with distributed-ring contact. Appl Optics 50 (7), 1034–1037 (2011) Zhou, D., Seurin, J.F., Pu, Z., Tong, C., Leeuwen, R.V.: Progress on high-power high-brightness VCSELs and applications. Proceedings of SPIE - The International Society for Optical Engineering 9381 , 93810B-93810B-93812: (2015a) Zhou, D.L., Seurin, J.F., Xu, G.Y., Miglo, A., Li, D.Z., Wang, Q., Sundaresh, M., Wilton, S., Matheussen, J., Ghosh, C.: Progress on vertical-cavity surface-emitting laser arrays for infrared illumination applications. Paper presented at the Vertical-cavity surface-emitting lasers XVIII, San Francisco, CA Zhou, D.L., Seurin, J.F., Xu, G.Y., Zhao, P., Xu, B., Chen, T., van Leeuwen, R., Matheussen, J., Wang, Q., Ghosh, C.: Progress on high-power, high-brightness VCSELs and applications. Paper presented at the Vertical-Cavity Surface-Emitting Lasers Xix, San Francisco, CA Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 15 Feb, 2022 Reviewers invited by journal 11 Feb, 2022 Editor invited by journal 06 Feb, 2022 Editor assigned by journal 20 Jan, 2022 First submitted to journal 19 Jan, 2022 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. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-1278067","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":83177920,"identity":"5b33ffdf-f382-4bbf-a948-2ab19b0bf83e","order_by":0,"name":"Congcong Wang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwklEQVRIiWNgGAWjYPACGx4DUrWkka7lMAPxWgyOnz384kfNeRlz9t4DDD9qGOTNCWo5k5dm2XPsNo9lz7kExp5jDIY7GwhoMTuQY2bM2HCbx+BGjgEDbwNDgsEBQlrOvwFpOcdjcP+NAeNforTcyDF+zNhwAGgLjwEzUbbY33hjBvRCMg/QUwmHZY5JGG4gpEWyP8f4w48aO3tg0B18+KbGRp6gLUDAJgGheRiAiiUIqwcC5g8wLaNgFIyCUTAKsAIAdu0/66lTyEYAAAAASUVORK5CYII=","orcid":"","institution":"Institute of High Energy Physics Chinese Academy of Sciences","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Congcong","middleName":"","lastName":"Wang","suffix":""},{"id":83177921,"identity":"3bedb51b-32ba-4c70-871d-bb88835c6ff9","order_by":1,"name":"Chong Li","email":"","orcid":"","institution":"Beijing University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Chong","middleName":"","lastName":"Li","suffix":""},{"id":83177922,"identity":"461602b9-7ab7-4200-903e-15b018b8ab81","order_by":2,"name":"Zhiyong Wang","email":"","orcid":"https://orcid.org/0000-0002-8751-9432","institution":"Beijing University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Zhiyong","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2022-01-20 02:33:32","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-1278067/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-1278067/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":18251231,"identity":"efdf4cbd-af45-43dc-a8ef-3e1ebad3bf64","added_by":"auto","created_at":"2022-02-15 18:13:14","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":49971,"visible":true,"origin":"","legend":"\u003cp\u003eSectional diagram of the VCSEL array\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-1278067/v1/0be90125bf0f6757ef906ae7.jpeg"},{"id":18250958,"identity":"07fb916c-4e91-4ab2-ab79-3b9f31e72741","added_by":"auto","created_at":"2022-02-15 18:10:15","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":87772,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic of experiment setup for (a) P-I-V and (b) far-field spot and spectrum\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-1278067/v1/48f8d09b5956728b5f139c25.jpeg"},{"id":18250954,"identity":"2a1339b4-6111-4de7-9633-53dbf20d8798","added_by":"auto","created_at":"2022-02-15 18:10:14","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":135984,"visible":true,"origin":"","legend":"\u003cp\u003eVCSEL: (a) Temperature-dependent threshold currents and slope efficiency. (b) Mode wavelength (MW) and gain peak wavelength (GPW).\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-1278067/v1/89aff4f58f7441ae183b3647.jpeg"},{"id":18250952,"identity":"01e6b4ec-8cab-4fe8-818e-8a40b3979a2c","added_by":"auto","created_at":"2022-02-15 18:10:14","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":126328,"visible":true,"origin":"","legend":"\u003cp\u003eVCSEL: (a) Temperature-dependent power and current (P-I-V) characteristics. (b) Power conversion efficiency (PCE) characteristics.\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-1278067/v1/3bdd0e0f9b02c5837ef1ab89.jpeg"},{"id":18250956,"identity":"e61ab161-144a-461a-b011-164ef2baa998","added_by":"auto","created_at":"2022-02-15 18:10:14","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":145876,"visible":true,"origin":"","legend":"\u003cp\u003e\u0026nbsp;2×2 VCSEL arrays (array spacing d=160 μm, 180 μm 200 μm): (a) Temperature-dependent power and current (P-I) characteristics. (b) Power conversion efficiency (PCE) characteristics.\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-1278067/v1/9f76a53ea6a84cec90934560.jpeg"},{"id":18251232,"identity":"058c459f-0f33-46bc-9065-83ab280e96c3","added_by":"auto","created_at":"2022-02-15 18:13:14","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":147840,"visible":true,"origin":"","legend":"\u003cp\u003e2×2 VCSEL array (d=200 μm) (a) Measured temperature-dependent emission wavelength (I=40mA). (b) Peak wavelength versus dissipated power at 20℃\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-1278067/v1/e6a1ff8a15eb3e7a9fbe0555.jpeg"},{"id":18250955,"identity":"1c2b4676-2d8c-41c5-ae77-fd743b978877","added_by":"auto","created_at":"2022-02-15 18:10:14","extension":"jpeg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":257786,"visible":true,"origin":"","legend":"\u003cp\u003e2×2 VCSEL arrays: Simulated temperature distribution and temperature curve along A-A’ cut-line in active region: (a) d=160 μm. (b) d=180 μm. (c) d=200 μm\u003c/p\u003e","description":"","filename":"floatimage8.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-1278067/v1/16fdaeda2272598c39c68bcf.jpeg"},{"id":18251234,"identity":"cd87963f-f832-4c16-aa6a-7a27c46c1695","added_by":"auto","created_at":"2022-02-15 18:13:17","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":733257,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-1278067/v1/7d77afc8-f1eb-4633-b552-0923d57cbd7d.pdf"}],"financialInterests":"","formattedTitle":"Analysis of optical and thermal properties of 940-nm vertical-cavity surface-emitting lasers","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eVertical-cavity surface-emitting lasers (VCSELs) have advantages of symmetrical laser beam, low threshold, high-speed modulation, single longitudinal mode, lack of catastrophic optical mirror damage (COMD), and simple arrangement in two dimensional arrays(Chuyu et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Lu et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Seurin et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Larisch et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Seurin et al. 2016; Tatsuo Hariyama et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). They have been used in optical interconnect, high-speed local-area networks parallel links, Gigabit Ethernet, atomic clock system, free-space data transmission, laser pumping and illumination field. Moreover, 940-nm VCSELs have been innovatively applied in the fields of three-dimensional (3D) face recognition, laser radar, automobile auxiliary driving, artificial intelligence robot and virtual reality/augmented reality (VR/AR) (Tatsuo Hariyama et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Yong-Qin et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Shichijo,Miyamoto \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Nazaruk et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). In laser pumping, laser radar, 3D sensing, illumination and other highly integrated fields need VCSEL with high output power and photoelectric conversion efficiency (PCE). In some extreme temperature conditions, temperature changes will seriously affect the performance of VCSELs. Extensive application in optical fiber sensing and core chip atomic clock system, require VCSELs with low threshold, wavelength stability and low temperature sensitivity(Derebezov et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Nishikata et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; HuiQing et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Tong \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2005\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSome scholars have studied the output power, PCE, beam quality and working stability of VCSEL. Moench H et al. reported the 808-nm VCSEL array combination with the photoelectric conversion efficiency (PCE) of up to 40% and output power of 9.6kW(Moench et al. 2014a; Moench et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2014b\u003c/span\u003e). Zhou D. L. et al investigated the 980-nm VCSEL array combination with photoelectric conversion efficiency of up to 40% and output power of 14kW(Zhou et al. 2015b; Zhou et al. 2014). Osram\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003epower of 1W(Iga,Kenichi 2018). Meng Xun et al. studied the 940-nm VCSEL array with output\u003c/p\u003e \u003cp\u003edeveloped the 940-nm VCSEL array with electro-optic conversion efficiency of up to 35% and output power of 210mW(Meng Xun et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Compared with the 808-nm and 980-nm VCSEL array, the performance of 940-nm VCSEL array is relatively poor. The internal thermal and thermal crosstalk effect of the VCSEL array is one of the most significant factors, which affect the output power and PCE. A high temperature will reduce the output characteristics and lifetime of VCSEL array. Heat sources of VCSEL consist of two parts: joule heating of DBR (especially P-DBRs) and heating of the active region. Compared with 808-nm VCSEL array, 940-nm VCSEL array produces more heat due to more P-distributed Bragg reflectors (DBRs). What is more serious is that top-emitted 940-nm VCSEL array has poor cooling effect compared with the bottom-emitted 980-nm VCSEL array.\u003c/p\u003e \u003cp\u003eIn this paper, our main attention will be focused on the photoelectric properties of 940-nm VCSEL and its arrays. Firstly, temperature dependence of threshold current, the output power and electro-optic conversion efficiency (PCE) of VCSEL were studied, and the mechanism of the minimum threshold current was analyzed in detail. Then, the output power and PCE of 2\u0026times;2 VCSEL arrays with different arrays spacing (d=160\u0026micro;m, 180\u0026micro;m and 200\u0026micro;m) were systematically analyzed. In addition, 3D thermoelectric coupling models were established based on finite element analysis to investigate the thermal distribution of 2\u0026times;2 VCSEL arrays.\u003c/p\u003e "},{"header":"2.\tFabrication","content":"\u003cp\u003eThe GaAs-based 940nm VCSEL epitaxial structure consists of 23 pairs Al\u003csub\u003e0.12\u003c/sub\u003eGa\u003csub\u003e0.88\u003c/sub\u003eAs/Al\u003csub\u003e0.9\u003c/sub\u003eGa\u003csub\u003e0.1\u003c/sub\u003eAs layers for the P-DBRs and 32 pairs Al\u003csub\u003e0.12\u003c/sub\u003eGa\u003csub\u003e0.88\u003c/sub\u003eAs/AlAs layers for the N-DBRs. The active region includes three strained 4.4-nm-thick In\u003csub\u003e0.16\u003c/sub\u003eGa\u003csub\u003e0.84\u003c/sub\u003eAs quantum wells (QWs) and four 6.2-nm-thick strain-compensating GaAs\u003csub\u003e0.92\u003c/sub\u003eP\u003csub\u003e0.08\u003c/sub\u003e barriers. The QWs with high In-content for wavelength extension and strain compensating GaAs\u003csub\u003e0.92\u003c/sub\u003eP\u003csub\u003e0.08\u003c/sub\u003e barriers for compressive strain in the QWs for high differential gain(Simpanen et al. \u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e). Carriers and photons are well-confined along the transverse direction by a 30nm thick Al\u003csub\u003e0.98\u003c/sub\u003eGa\u003csub\u003e0.02\u003c/sub\u003eAs oxide aperture on the P-DBRs. The top-emitted 940-nm VCSEL array chip fabrication is as follows. First, etched circular top mesas just through the optical cavity with Cl\u003csub\u003e2\u003c/sub\u003e + BCl\u003csub\u003e3\u003c/sub\u003e in an inductively coupled plasma (ICP) reactive ion etching to expose high Al content layer. Then oxide aperture (\u0026Phi;\u0026thinsp;=\u0026thinsp;10 \u0026micro;m) was formed by the selective wet oxidation of Al\u003csub\u003e0.98\u003c/sub\u003eGa\u003csub\u003e0.02\u003c/sub\u003eAs to Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e at temperature of 430℃. Ti/Au mental contact was deposited on the top of wafer by using electron beam evaporation system. SiN layer was deposited to form an insulating layer. After the GaAs substrate was thinned to 150\u0026micro;m, the Ni/Au/Ge/Ni/Au mental contact was deposited on the bottom of wafer by using measurement and control sputtering system. Finally, the contacts were rapidly annealed at 435 ℃. Figure. 1 shows the sectional diagram of VCSEL array.\u003c/p\u003e"},{"header":"3. Results And Discussion","content":"\u003cp\u003eThe VCSEL arrays were tested on a probe station using a semiconductor parameter analyzer (Keithley 4200), a high precision current source (Keithley 2430), a laser beam profiler (Spiricon SP928), a power meter (Thorlabs S120C) and a spectrograph (Yokogawa AQ6370D). A thermo electric cooler (TEC) can control the temperature vary from -30℃ to 40℃. Figure. 2 shows schematics of experiment setup in our experiment. All the performance parameters of VCSELs are obtained by on-chip test under continuous wave condition without extra heat dissipation solution.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a) showed the temperature-dependent threshold currents (I\u003csub\u003eth\u003c/sub\u003e) and slope efficiency for top-emitting VCSEL. And the relationship of threshold currents and temperature meets the parabolic equation (1). Under the same condition of injection current, operating temperature affects the threshold current and slope efficiency. As the operating temperature rises, the internal temperature of the device increases, which results in a reduction in output power and power conversion efficiency (PCE). As is shown in the figure. 3(a), the threshold current decreases at first and then increases as the temperature increases in the case-temperature range from -30 ℃ to 40℃. The minimum threshold currents (I\u003csub\u003eth, min\u003c/sub\u003e) of 10-\u0026micro;m oxide aperture VCSEL was 0.995mA, when the environment temperature was 20℃.\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$${I}_{th}\\left(T\\right)={I}_{th},\\text{m}\\text{i}\\text{n}\\times \\left[1+{C}_{T}{\\left(T-{T}_{min}\\right)}^{2}\\right] \\left(1\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere C\u003csub\u003eT\u003c/sub\u003e is a constant, C\u003csub\u003eT\u003c/sub\u003e=9.16\u0026times;10\u003csup\u003e\u0026minus;5\u003c/sup\u003e; T\u003csub\u003emin\u003c/sub\u003e is the temperature of the minimum threshold current, T\u003csub\u003emin\u003c/sub\u003e=19.3℃; I\u003csub\u003eth, min\u003c/sub\u003e is the minimum threshold current, I\u003csub\u003eth, min\u003c/sub\u003e=1mA; I\u003csub\u003eth\u003c/sub\u003e(T) is the threshold current in different temperature (T).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe mode wavelength (MW) and gain peak wavelength (GPW) of VCSEL are two main factors that affect the threshold current of VCSEL. In order to study the physical mechanism of VCSEL threshold current generation, the reflection spectrum of DBR (contains P-DBR and N-DBR) and gain spectrum of active region were simulated using TFCalc and Crosslight software under the operating temperature of -30℃ ཞ 40℃. The reflectivity spectrums were calculated by transfer matrix method. Among them, the minimum point in the reflection spectrum corresponds to the resonance condition, so the mode wavelength can be obtained from the reflection spectrum of VCSEL(Wang et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1995\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFigure. 3(b) showed the mode wavelength (MW) and gain peak wavelength (GPW) of the 10\u0026micro;m VCSEL (10mA) under the operating temperature of -30℃ ཞ 40℃. With the increase of temperature, the mode wavelength and gain peak wavelength of VCSEL were redshift. The redshift rate of mode wavelength is 0.0557 nm/℃. As is known, the mode wavelength of a VCSEL is determined by the cavity resonance due to the short optical resonator. The wavelength shift mainly depends on changes of the average refractive index in the resonator(Michalzik \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). The redshift rate of gain peak wavelength is 0.33 nm/℃. As the temperature increases, the crystal lattice constant increases. This leads to a weakening of the binding effect of the valence electron period potential. The energy required for the valence electron transition decreases and the band gap shrinks. Bandgap shrinkage causes gain peak wavelength redshift. The peak gain decreases as the temperature increases, due to electron occupancy probability near the Fermi level is smoothness. A minimum threshold current of a VCSEL value exists, when the gain wavelength is the same as the mode wavelength at a temperature of 20\u0026deg;C, due to temperature-dependent gain and mode wavelength shifts. The physical mechanism of VCSEL threshold current generation was verified by combining theory and experiment.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure. 4 showed the measured (a) temperature-dependent power, current, voltage (P-I-V) and (b) PCE characteristics of 10\u0026micro;m VCSEL. As is shown in figure. 4(a), the maximum output power is 13.5mW at -30\u0026deg;C and decreases to 9.6mW at 40\u0026deg;C. The slope efficiency is 1.17 W/A at -30\u0026deg;C and decreases to 0.98 W/A at 40\u0026deg;C. With the temperature increases, electron hole non-radiative recombination especially auger recombination is strengthened. More electric energy is released in the form of phonons, internal losses increasing with the temperature, which leads to a decrease of the differential efficiency and output power. Lower carrier concentration and higher carrier mobility can reduce the differential resistance. With the increase of temperature, the carrier concentration in the active region increases, and the probability of collision between carriers and ionized impurities increases, which leads to the decrease of carrier mobility. Temperature-dependent I-V curve means that the differential resistance of VCSEL was decreased with temperature increasing. This result indicates that the main factor determining differential resistance of VCSEL is the carrier concentration in the active region, and the secondary factor is the carrier mobility.\u003c/p\u003e \u003cp\u003eAs is shown in figure. 4(b), when the injection current is about 5mA, the PCE reaches the maximum value. Among them, the highest efficiency can reach 48% at 20\u0026deg;C. When the injection current is about 13.5mA, laser power density is up to 17kW/cm\u003csup\u003e2\u003c/sup\u003e at -30\u0026deg;C. To examine the beam property, the far-field patterns of the VCSEL at 20\u0026deg;C were measured at a distance of 50 mm from the VCSEL surface by a laser beam profiler. The far-field beam profile is symmetric and the intensity is near uniform, the far-field divergence angle is 23\u0026deg; at 13.5 mA.\u003c/p\u003e \u003cp\u003eThrough the above experiments, we found that 10-\u0026micro;m oxide aperture VCSEL has higher electro-optical conversion efficiency and power density, but overall output power was low. In order to improve the output power of VCSELs, the photoelectric performances of 2\u0026times;2 and 2\u0026times;4 VCSEL arrays with oxidation aperture of 10\u0026micro;m were studied systematically.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure. 5 shows the output power and PCE of 2\u0026times;2 VCSEL arrays. As the VCSEL array spacing (d) is 200\u0026micro;m, the maximum PCE was 47.2% at -30 ℃ and decreased to 40.06% at 40 ℃; the maximum power was 48.72mW at -30 ℃ and decreased to 32.93% at 40 ℃. Full width half maximum (FWHM) was 1.05nm at -30 ℃ and decreased to 1.42nm at 40 ℃, respectively. The spectral broadening rate is only 0.0053nm/℃. The beam distribution is relatively uniform, and the divergence angle is about 20\u0026deg;. With increasing temperature and the decrease of the array spacing, the output power and PCE show a downward trend. The main cause of this phenomenon is heat accumulation caused by thermal resistance effect. In addition, in order to increase the power of the VCSEL array, the 2\u0026times;4 VCSEL array (d=200 \u0026micro;m) was prepared, and the maximum power and PCE were 90.8mW and 40% at -30 ℃, respectively. The spectral broadening rate is 0.007nm/K. The above measured data conform that device exhibited superior adaptability to high and low temperatures operation characteristics.\u003c/p\u003e \u003cp\u003eIn order to analyze the thermal effect of VCSEL, its thermal resistance of can be obtained from the emission spectra and dissipated power. The thermal resistance equation (2) is(Zhou et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2015a\u003c/span\u003e)\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$${R}_{th}=\\frac{\\varDelta T}{\\varDelta {P}_{diss}}=\\frac{\\varDelta \\lambda /\\varDelta {P}_{diss}}{\\varDelta \\lambda /\\varDelta {T}_{a}} \\left(2\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e∆P\u003csub\u003ediss\u003c/sub\u003e is the dissipated power. The dissipated power is equal to injected electrical power subtracting output optical power. ∆λ/∆P\u003csub\u003ediss\u003c/sub\u003e is calculated by variation of the wavelength shift with the variation of the dissipated power (Zhou et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2015a\u003c/span\u003e). ∆λ is the wavelength shift rate, ∆T\u003csub\u003ea\u003c/sub\u003e is the varied ambient temperature.\u003c/p\u003e \u003cp\u003eThe thermal resistance was obtained by analyzing the experimental photoelectric performance parameters of 2\u0026times;2 VCSEL array (d=200\u0026micro;m). Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a) shows the measured temperature-dependent emission wavelength, the wavelength shifts with ambient temperature linearly by a rate of 0.054 nm/℃. The relationship between peak wavelength and dissipated power is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(b), which obtained by measuring the emission spectra under different injection currents at ambient temperature of 20 ℃. When the injection current was 40mA, ∆λ/∆P\u003csub\u003ediss\u003c/sub\u003e is 0.028 nm/mW. The dissipated power (P\u003csub\u003ediss\u003c/sub\u003e) is 70mW. According to (2), the thermal resistance is 0.515 ℃/mW. The equation of actual temperature in active region (T\u003csub\u003eac\u003c/sub\u003e) is as follows: T\u003csub\u003eac\u003c/sub\u003e=T\u003csub\u003ea\u003c/sub\u003e+ R\u003csub\u003eth\u003c/sub\u003eP\u003csub\u003ediss\u003c/sub\u003e. In this case, the actual temperature in active region is 56.04 ℃.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn order to analyze the thermal distribution of 2\u0026times;2 VCSEL arrays (d=160\u0026micro;m, 180\u0026micro;m and 200\u0026micro;m), a 3D thermoelectric coupling model based on finite element analysis was established by COMSOL Multiphysics. In this model, the equivalent structure method is adopted to simulate the VCSEL structure, whose structure mainly includes: P-DBR, active region, N-DBR and GaAs substrate. Joule heat and heat generation in active region are two main sources of VCSEL heat generation. The resistance is generated by the VCSEL heterojunction barrier structure and the parasitic resistance of the VCSEL array, interact with the current to produce a large amount of joule heat. The carrier injection, carrier leakage, carrier recombination and absorption loss occurring in the active region will generate a large amount of heat, which becomes the main heat source of the active region. In this model, the ambient temperature is set to 20℃ and the injection current of each light source is set to 10mA.\u003c/p\u003e \u003cp\u003eFigure. 7 shows the simulated temperature distributions and temperature curve along A-A\u0026rsquo; cut-line in active region. As is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, the maximum temperatures in active region were 63.1 ℃ @160\u0026micro;m, 59.1℃@180\u0026micro;m and 55.9℃@200\u0026micro;m, respectively. When the array spacing is 200\u0026micro;m, the simulation results are consistent with the actual results, which proves the correctness of the simulation results. According to the above experimental results, optimizing the thermal accumulation of devices can improve the output power and PCE. Therefore, in order to obtain high-power VCSEL, it is necessary to optimize the epitaxial structure, such as reasonably increasing doping concentration, designing gradual DBR structure and reduce the pairs of DBRs. The DBRs have gradient composition interfaces and are modulation doped for efficient transport of carriers across the interfaces and low internal optical loss(Simpanen et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). In order to improve the heat dissipation performance of the device, the device can use the 3D micro-channel heat sink of tungsten copper alloy with Pin Fin structure to conduct water cooling heat dissipation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"4. Conclusion And Perspectives","content":"\u003cp\u003eIn summary, the physical mechanism of minimum threshold current generation in oxide-confined VCSEL has been thoroughly studied theoretically and experimentally. That is, the threshold current reaches the minimum value when the mode wavelength matches the gain wavelength. VCSEL with an oxide aperture diameter φ\u0026sim;10 \u0026micro;mexhibit 13.5 mW operating optical output power and 1.17 W/A slope efficiency at -30\u0026deg;C. And its highest PCE and laser power density are up to 48% at and 17kW/cm\u003csup\u003e2\u003c/sup\u003e. The 2\u0026times;2 VCSEL array (d=200\u0026micro;m) exhibit the maximum PCE was 47.2% at -30 ℃ and decreased to 40.06% at 40 ℃; the maximum power was 48.72mW at -30 ℃ and decreased to 32.93% at 40 ℃. Full width half maximum (FWHM) was 1.05nm at -30 ℃ and increased to 1.42nm at 40 ℃, respectively. The spectral broadening rate is only 0.0053nm/℃. The 2\u0026times;4 VCSEL array (d=200\u0026micro;m) exhibit the maximum power was 90.8 mW at -30 ℃. We find an increase in output power and PCE of 2\u0026times;2 VCSEL array as we increase the array spacing which we attribute primarily to increased heat dissipation and reduced thermal crosstalk between the emitters. Thermal properties in oxide-confined 2\u0026times;2 VCSEL arrays were analyzed numerically and experimentally. The simulated results agree well with the measurement. It is proved that theoretical simulation is very useful for the future device optimization.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThis work was supported in part by the National Natural Science Foundation (61505003, 61674140) and Beijing education commission project (SQKM201610005008).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003e\u003cspan\u003eChuyu, Z., Xing, Z., Di, L., Yongqiang, N., Lijun, W.: Enhanced thermal stability of VCSEL array by thermoelectric analysis-based optimization of mesas distribution. Chin. Phys. B \u003cstrong\u003e26\u003c/strong\u003e(06), 157\u0026ndash;164 (2017)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eDerebezov, I.A., Haisler, V.A., Bakarov, A.K., Kalagin, A.K., Toropov, A.I., Kachanova, M.M., Gavrilova, T.A., Semenova, O.I., Tretyakov, D.B., Beterov, I.I., Entin, V.M., Ryabtsev, I.I.: Single-mode vertical-cavity surface emitting lasers for 87Rb-based chip-scale atomic clock. Semiconductors+ \u003cstrong\u003e44\u003c/strong\u003e(11), 1422\u0026ndash;1426 (2010)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eHuiQing, L., Jie, Z., DaFu, C., ZuYan, X., YongQiang, N., ChangLing, Y., Li, Q., Yun, L., LiJun, W., JianLin, C.: Optimal designs for high-power vertical cavity surface emitting lasers. Acta Physica Sinica \u003cstrong\u003e53\u003c/strong\u003e(9), 2986\u0026ndash;2990 (2004)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eIga, K.: Forty years of vertical-cavity surface-emitting laser: Invention and innovation. Jpn. J. Appl. Phys. \u003cstrong\u003e57\u003c/strong\u003e(8), 08PA01 (2018)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eLarisch, G., Moser, P., Lott, J.A., Bimberg, D.: Impact of Photon Lifetime on the Temperature Stability of 50 Gb/s 980 nm VCSELs. Ieee Photonic Tech L \u003cstrong\u003e28\u003c/strong\u003e(21), 2327\u0026ndash;2330 (2016)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eLu, H.H., Li, C.Y., Chu, C.A., Lu, T.C., Chen, B.R., Wu, C.J., Lin, D.H.: 10 m/25 Gbps LiFi transmission system based on a two-stage injection-locked 680 nm VCSEL transmitter. Opt Lett \u003cstrong\u003e40\u003c/strong\u003e(19), 4563\u0026ndash;4566 (2015)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eMeng Xun, G., Pan, Z., Zhao, Y., Sun, C., Yang, Kan, Q.: Analysis of Thermal Properties of 940-nm Vertical Cavity Surface Emitting Laser Arrays. IEEE TRANSACTIONS ON ELECTRON DEVICES \u003cstrong\u003e68\u003c/strong\u003e(1), 158\u0026ndash;163 (2021)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eMichalzik, R.: VCSELs, vol.\u0026nbsp;166. Fundamentals, Technology and Applications of Vertical-Cavity Surface-Emitting Lasers. Springer-Verlag, Berlin Heidelberg (2013)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eMoench, H., Andreadaki, A., Gronenborn, S., Kolb, J.S., Loosen, P., Miller, M., Schwarz, T., van der Lee, A., Weichmann, U.: High power electrically pumped VECSELs and arrays. Paper presented at the Vertical External Cavity Surface Emitting Lasers (Vecsels) Iv, San Francisco, CA\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eMoench, H., Kolb, J.S., Engelhardt, A.P., Gerlach, P., Witzigmann, B.: Optimized VCSELs for high-power arrays. Proceedings of SPIE \u003cstrong\u003e9001\u003c/strong\u003e(3), 395-406: (2014b)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eNazaruk, D.E., Blokhin, S.A., Maleev, N.A., Bobrov, M.A., Kuzmenkov, A.G., Vasil\u0026apos;ev, A.P., Gladyshev, A.G., Pavlov, M.M., Blokhin, A.A., Kulagina, M.M., Vashanova, K.A., Zadiranov, Y.M., Fefelov, A.G., Ustinov, V.M.: Single-mode temperature and polarisation-stable high-speed 850nm vertical cavity surface emitting lasers. J Phys Conf Ser \u003cstrong\u003e572\u003c/strong\u003e, 012036 (2014). doi:Unsp 012036\u0026nbsp;\u003c/span\u003e\u003cspan\u003e1088/1742-6596/572/1/012036\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eNishikata, K., Yokouchi, N., Koyama, F.: Wide temperature operation of 850-nm VCSEL and isolator-free operation of 1300-nm VCSEL for a variety of applications. Proceedings of SPIE - The International Society for Optical Engineering \u003cstrong\u003e5737\u003c/strong\u003e, 8-19: (2005)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eSeurin, J.-F., Zhou, D., Xu, G., Miglo, A., Li, D., Chen, T., Guo, B., Ghosh, C.: High-efficiency VCSEL arrays for illumination and sensing in consumer applications. Paper presented at the Conference on Vertical-Cavity Surface-Emitting Lasers XX, San Francisco, CA\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eSeurin, J.F., Xu, G.Y., Wang, Q., Guo, B.M., Van Leeuwen, R., Miglo, A., Pradhan, P., Wynn, J.D., Khalfin, V., Ghosh, C.: High-brightness pump sources using 2D VCSEL arrays. Vertical-Cavity Surface-Emitting Lasers Xiv \u003cstrong\u003e7615\u003c/strong\u003e: (2010). doi:Artn 76150f\u0026nbsp;\u003c/span\u003e\u003cspan\u003e1117/12.842492\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eShichijo, T., Miyamoto, T.: Rate equation-based numerical analysis of mutual injection for phase locked 2D-VCSEL array using Talbot effect. Jpn. J. Appl. Phys. \u003cstrong\u003e58\u003c/strong\u003e(1), SJJC01 (2019)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eSimpanen, E., Gustavsson, J.S., Larsson, A., Karlsson, M., Sorin, W.V., Mathai, S., Tan, M.R., Bickham, S.R.: 1060 nm Single-Mode VCSEL and Single-Mode Fiber Links for Long-Reach Optical Interconnects. J Lightwave Technol \u003cstrong\u003e37\u003c/strong\u003e(13), 2963\u0026ndash;2969 (2019)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eTatsuo Hariyama, P.A.M., Sandborn, M., Watanabe, Wu, M.C.: High-accuracy range-sensing system based on FMCW using low-cost VCSEL. Opt. Express \u003cstrong\u003e26\u003c/strong\u003e(7), 9285 (2018)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eTong, C.Z.: Design and analysis of 1.3 \u0026micro;m GaAs-based quantum dot vertical-cavity surface-emitting lasers. Acta Physica Sinica \u003cstrong\u003e54\u003c/strong\u003e(8), 3651\u0026ndash;3656 (2005)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eWang, H., Xu, W., Cheng, Q., Ji, Z., Gao, R., Wu, P., Xu, Z.: Phase-Locking of a Gunn Oscillator at 3 mm Waveband Using High Temperature Superconducting Josephson Junction Harmonic Mixer. Chin. Phys. Lett. \u003cstrong\u003e12\u003c/strong\u003e(4), 253 (1995)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eYong-Qin, H., Yan, L., Yuan, F., Chang-Ling, Y., Ying-Jie, Z., Yu-Xia, W., Xiao-Hua, W., Yi, Q., Guo-Jun, L.: Large aperture vertical cavity surface emitting laser with distributed-ring contact. Appl Optics \u003cstrong\u003e50\u003c/strong\u003e(7), 1034\u0026ndash;1037 (2011)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eZhou, D., Seurin, J.F., Pu, Z., Tong, C., Leeuwen, R.V.: Progress on high-power high-brightness VCSELs and applications. Proceedings of SPIE - The International Society for Optical Engineering \u003cstrong\u003e9381\u003c/strong\u003e, 93810B-93810B-93812: (2015a)\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eZhou, D.L., Seurin, J.F., Xu, G.Y., Miglo, A., Li, D.Z., Wang, Q., Sundaresh, M., Wilton, S., Matheussen, J., Ghosh, C.: Progress on vertical-cavity surface-emitting laser arrays for infrared illumination applications. Paper presented at the Vertical-cavity surface-emitting lasers XVIII, San Francisco, CA\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eZhou, D.L., Seurin, J.F., Xu, G.Y., Zhao, P., Xu, B., Chen, T., van Leeuwen, R., Matheussen, J., Wang, Q., Ghosh, C.: Progress on high-power, high-brightness VCSELs and applications. Paper presented at the Vertical-Cavity Surface-Emitting Lasers Xix, San Francisco, CA\u003c/span\u003e\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"optical-and-quantum-electronics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"oqel","sideBox":"Learn more about [Optical and Quantum Electronics](https://www.springer.com/journal/11082)","snPcode":"11082","submissionUrl":"https://submission.nature.com/new-submission/11082/3","title":"Optical and Quantum Electronics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"VCSEL arrays, the minimum threshold current, power, thermal properties","lastPublishedDoi":"10.21203/rs.3.rs-1278067/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-1278067/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eWe achieve 13.5mW optical output power, 48% power conversion efficiency, 1.17 W/A slope efficiency and 17kW/cm\u003csup\u003e2\u003c/sup\u003e laser power density with top-surface-emitting 940 nm oxide-confined vertical-cavity surface-emitting laser (VCSEL). The physical mechanism of minimum threshold current generation in oxide-confined VCSEL has been thoroughly studied theoretically and experimentally. Further, we also succeeded in 90.8mW optical output power, 40% power conversion efficiency with 2\u0026times;4 VCSEL arrays. We find an increase in output power and PCE of 2\u0026times;2 VCSEL arrays as we increase the array spacing which we attribute primarily to increased heat dissipation and reduced thermal crosstalk between the emitters. Thermal properties in oxide-confined 2\u0026times;2 VCSEL arrays were analyzed numerically and experimentally. The simulated results are in good agreement with the measurement. It is proved that theoretical simulation is very useful for the future device optimization.\u003c/p\u003e","manuscriptTitle":"Analysis of optical and thermal properties of 940-nm vertical-cavity surface-emitting lasers","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-02-15 18:10:12","doi":"10.21203/rs.3.rs-1278067/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2022-02-15T07:16:37+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2022-02-11T13:45:17+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Optical and Quantum Electronics","date":"2022-02-06T14:49:36+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2022-01-20T07:43:51+00:00","index":"","fulltext":""},{"type":"submitted","content":"Optical and Quantum Electronics","date":"2022-01-19T21:33:05+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"optical-and-quantum-electronics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"oqel","sideBox":"Learn more about [Optical and Quantum Electronics](https://www.springer.com/journal/11082)","snPcode":"11082","submissionUrl":"https://submission.nature.com/new-submission/11082/3","title":"Optical and Quantum Electronics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"56748071-2af1-4250-b9d7-6ce3e63a2163","owner":[],"postedDate":"February 15th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2022-05-05T14:15:48+00:00","versionOfRecord":[],"versionCreatedAt":"2022-02-15 18:10:12","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-1278067","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-1278067","identity":"rs-1278067","version":["v1"]},"buildId":"ehx78VzkSd0WSzXnipQa-","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}