In this work, a high-performance mid-wave infrared (MWIR) photodetector (PD) utilizing an InAs/GaSb Type-II superlattice absorber and a quaternary AlGaAsSb barrier is designed and analyzed based on numerical simulations aimed at determining an optimized detector structure. Through these simulations, the composition of the AlGaAsSb barrier is carefully designed to achieve lattice matching, high conduction band offset and zero valence band offset. By optimizing the barrier thickness and doping concentration, the depletion region is effectively shifted from the narrow-bandgap absorber to the wide-bandgap barrier; additionally, at 150 K and a reversed bias of 0.05 V, the dark current density in the PD with the barrier (pBn) is reduced to 1.83 & times; 10-5 A/cm2, about two orders of magnitude lower than that of the PD without the barrier. Furthermore, the effect of the barrier on the generation-recombination (G-R) and the trap-assisted tunneling (TAT) currents are analyzed and compared in detail, and it is found that the barrier structure is much more effective in suppressing the TAT current at low reversed bias when the electric field is low in the absorber layer. These results demonstrate the efficacy of the proposed AlGaAsSb barrier design for realizing high-operating-temperature MWIR PDs. It also provides an insight into the physical mechanism that leads to the performance enhancement of InAs/GaSb PDs.

For the high-performance InGaAs focal plane arrays (FPAs), the photosensitive pixels with abnormal noise behavior restrict the quality of the captured short-wave infrared (SWIR) image. The blind pixels arranged in the cross pattern was systemically studied in this work. The dark current of the central pixel of the cross blind pixels was observed with a dramatic increase, resulting in the deteriorated performance under long integration times (Tint), even under the cooling condition. The surrounding pixels also exhibit high noise under longer Tint. Noise component extraction reveals that under longer Tint, the noise of cross blind pixels is dominated by 1/f noise, which can be attributed to the surface states from local defects on the passivation interface. And the thermal noise and shot noise significantly increase with different levels. According to blackbody radiation measurements, the signal response of noise blind pixels remains equal to that of the normal pixels. Statistical noise analysis of the entire FPA demonstrates that the cross noise blind pixels are a critical factor limiting the performance of FPA under long Tint.

Temperature-dependent laser beam-induced current (LBIC) measurements were carried out on planar In0.53Ga0.47As PIN photodetectors under both front-side and cross-sectional illumination over the range of 88-296 K. Combined with diffusion-mechanism simulations, the temperature-dependent carrier transport behavior under the two illumination configurations was analyzed comparatively. Opposite temperature dependences were observed in the extracted diffusion length, with the cross-sectional value increasing from 22.52 & micro;m at 273 K to approximately 125 & micro;m at 123 K, whereas the front-side value decreased from 18.69 & micro;m to 10.81 & micro;m. This difference is likely associated with the distinct carrier transport paths involved in the two configurations. The simulation results further suggest that the low-temperature attenuation of the front-side LBIC response is likely associated with the heterojunction barrier, while the built-in electric field provides only limited compensation. Overall, cross-sectional LBIC appears to more directly reflect intrinsic carrier transport in the InGaAs absorption layer.

A localized parasitic offset is observed on Sample A-1, a 488 × 1360 format InGaAs FPA under long integration time at 150 K. The tested 2.2 μm device achieves an ultralow dark current density of 0.059nA/cm2. The parasitic offset reaches 110 mV at 400 ms, with extra equivalent photocurrent of around 2 fA per pixel. Sample A-2 from the same fabrication batch contains less residual epoxy, and its abnormal stray signal is significantly suppressed. Time-sharing control experiments carried out on Sample A-3 confirm that cutting off power to output buffers during integration eliminates observable luminescence, which directly confirms the light source originates from output amplifiers. Variable-temperature measurements at 120 K, 150 K and 180 K further reveal that circuit glow can only be clearly distinguished under ultra-low dark current at low temperature, and will be submerged by high intrinsic dark current at higher temperatures. Experiments confirm the stray interference originates from electroluminescence of ROIC output buffers, where 1–2 mA static current flows through each Vout buffer unit. The light transmits via residual epoxy and reflects off gold-plated sapphire substrates. We propose a full metal shielding layout for output circuits. On a 3000 × 1000 2.2 μm FPA, no such localized parasitic offset can be detected under our test conditions. This work identifies a coupling path involving ROIC luminescence, epoxy scattering and substrate reflection, and demonstrates a practical layout solution for high-performance space-borne InGaAs FPAs

Achieving a high-aspect-ratio, high-uniformity indium bump array with a 5 mu m pitch through physical vapor deposition hinges on two critical factors: delaying photolithography pattern closure to suppress edge overgrowth and enhance aspect ratio, and reducing indium film roughness to improve array uniformity. Based on film growth theory, this study developed a method to determine the optimal parameters for indium bump growth by analyzing the initial growth characteristics and evolution of the indium film, surface roughness in non-patterned areas, and the extent of photolithography pattern occlusion in patterned areas. Through precise control of substrate temperature and deposition rate during thermal evaporation, we characterized the growth behavior of indium film at both initial and final stages under various parameter combinations, and established correlations between initial film stage growth characteristics and indium bump morphology, thereby enabling rapid iterative optimization of bump growth.

To fabricate high-performance InGaAs infrared detectors, this paper employs metal-organic chemical vapor deposition (MOCVD) to prepare detectors on InAs0.6P0.4/In0.8Ga0.2As/InAs0.6P0.4 double-hetero structure materials, achieving a cutoff wavelength of 2.54 mu m. The photoelectric response characteristics of the detector were studied. Firstly, the performance differences of detectors with traditional structure and different grille-pixel structures are studied. Compared with the conventional structure, the average dark current density of the grille-pixel structures detector was reduced by 52.6%. Through the analysis of the dark current density components, the grille-pixel structure detector reduced the dark current density by suppressing the generation-recombination current density and the trap-assisted tunneling current density. Secondly, at room temperature, the peak detectivity of the detector of conventional structure is 4.58 & times; 1010 cm Hz1/2/W, while the average peak detectivity of the detectors of grille-pixel structure increases to 6.05 & times; 1010 cm Hz1/2/W, an increase of approximately 32%. Overall, the grille-pixel structure has successfully enhanced the critical performance of the detector.

This study developed wet chemical etchants for evaluating dislocation density in extended-wavelength InGaAs photodetector materials. A systematic comparison of various etchants was conducted to assess their effectiveness in revealing dislocation-related etch pits on the material surface. An HF-H2O2 based etchant was specifically developed for extended-wavelength InGaAs photodetector materials. The ratio of the etchant components was optimized to enable reliable dislocation density evaluation, even for samples with very low defect densities. This etchant offers a practical and efficient approach for quality control and failure analysis during the development of advanced infrared photodetectors.

The optoelectronic properties of infrared detectors lie in the uniformity of semiconductor film materials. Effects of InP substrate roughness nonuniformity on the homogeneity of surface morphology, lattice structure, optical property and minority-carrier lifetime of wavelength extended InGaAs epitaxial material grown via molecular beam epitaxy (MBE) are investigated. Moreover, the direct correlation between epitaxial material nonuniformity and detector focal plane signal response is also assessed. Results show that under strict macroscopic control of growth parameters, slight nonuniformity of the substrate roughness will be amplified and cause a significant deterioration in the lattice quality, optical and electrical properties of epitaxial layers. The strong spatial correlation between the minority-carrier lifetime of the epilayer and the detector response nonuniformity underscores the critical, and previously underappreciated, role of substrate roughness uniformity in achieving high-performance lattice-mismatched infrared detectors.

Improved sensitivity of planar type extended-wavelength In0.75Ga0.25As/InP photodetectors is realized via post-diffusion rapid thermal annealing (RTA) treatment. The photoluminescence (PL) and x-ray diffraction characterizations are undertaken prior- and post- RTA treatments for a series of recipes with temperatures ranging from 500 to 750 degrees C and with durations of 15 and 30 s. While the dark current density at -10 mV decreases from 8.3 to 5.9 nA/cm(2) at 150 K for the RTA-processed sample as compared with the reference sample, the peak detectivity also rises from 9.0 & times; 10(9) to 2.0 & times; 10(10) cm Hz(1/2) W-1 at 150 K. Moreover, the cutoff wavelength remains unchanged whereas the strain of the lattice-mismatched epilayers tends to further relax post the RTA treatment. RTA temperatures higher than 750 degrees C leads to strong degradation of the PL intensity and fail of the photodetector. These results suggest that post-diffusion RTA is a feasible approach for the crystal lattice improvement of planar type extended-wavelength InxGa1-xAs (0.53 < x < 1) photodetectors.

Large dark currents currently limit the performance of InGaAs short-wave infrared (SWIR) detectors in aerospace remote sensing and night vision applications. To address this issue, SWIR detectors featuring various absorption layer doping concentrations and bilateral electrode configurations were fabricated on lattice-matched NIN InP/InGaAs/InP double heterojunctions via metal-organic chemical vapor deposition (MOCVD). Experimental and TCAD two-dimensional simulations demonstrate that increasing the absorption layer doping is the dominant factor, significantly reducing the total dark current density by ~96%. Mechanistic analysis indicates that increased doping in the absorption layer narrows the depletion region and prolongs the minority carrier lifetime, effectively suppressing both generation-recombination and trap-assisted tunneling currents. Concurrently, the bilateral electrode design distributes the electric field more uniformly, providing a further reduction in overall leakage. Furthermore, spectral analysis reveals that doping-modulated built-in electric fields lead to differentiated carrier collection mechanisms across varying wavelength bands. Ultimately, the optimized device achieves a peak detectivity of 2.28 × 1012 cm·Hz1/2W-1, representing an 82% improvement over low-doped counterparts and providing a crucial theoretical basis for the design of high-performance InGaAs detectors.

InGaAs/InP single-photon avalanche photodiode (SPAD) with a triple-step diffusion morphology is designed and fabricated. The avalanche probability distribution evolves from a toroidal shape to a Gaussian-like shape as compared with the conventional double-step diffusion. Free-running measurements indicate that the photon detection efficiency of the triple-step SPAD increases from 3.4% to 11% in comparison with a double-step SPAD with the same thickness of the avalanche region and under the same conditions. Meanwhile, the dark count rate (DCR) and the afterpulsing probability (APP) are also decreased from 820 to 25 kHz and from 80% to 43% under a hold-off time of $8 mu s, respectively. Consistently higher activation energies of both the dark current and the DCR are obtained for the triple-step SPAD, tentatively attributed to the evolvement of the dominant source of dark carriers from the thermal generation in the InGaAs absorber to the trap-assisted tunneling in the InP multiplier. Theoretical simulations indicate a faster detrapping time of carriers within the avalanche region accounts for the reduced APP for the triple-step SPAD with a higher peak E-field.

In this study,the simulation analysis and optimization of stray radiation in deep cryogenic Dewar components were conducted using a multiwave common optical path Dewar infrared system.The thermal radiation effects on the detector from key surfaces at different temperatures were analyzed using temperature field and dichroic surface simulations.Suitable cold transmission materials were selected,and Kovar was used for the cold platform,cold screen,and dichroic holder of the Dewar system.The effects of different blade levels and surface treatments of the cold screen on the point source transmittance were also evaluated.Based on these findings,the following optimization scheme was proposed:an elevated cold screen to block most of the radiation emitted or reflected by the window cap,adopting two levels of blades for the cold screen,and spraying graphene on the inner surface of the cold screen to improve the suppression of stray radiation.This scheme provides both theoretical and practical value for the design and application of low-temperature Dewar modules.

256 x 2 InGaAsP/InP Geiger-mode avalanche photodiode (GmAPD) arrays and a matched readout circuit with a triple-stage timing to digital converter (TDC) are realized. Pixels run asynchronously within the range gate of each frame, allowing measuring the time of flight of up to three reflected laser echoes. A mean array timing precision of 1 ns and a minimum hold-off time (T-hoff) of 64 ns are achieved. The measured mean dark count rates are 2.5, 1.0 and 0.5 kHz for the first, the second and the third stage TDC, respectively, under a mean photon detection efficiency (PDE) of 33.1% at 1064 nm, -20 degrees C and a T-hoff of 320 ns. While the cumulative afterpulsing probability (APP) exhibits strongly V-o- and T-hoff-dependent behaviors and a temperature-insensitive nature from -20 degrees C to 20 degrees C, a cumulative APP of 15% is obtained under a PDE of 20% and a T-hoff of 1 mu s. Photon count rate measurements indicate trade-off between the photon blockage and the increased afterpulsing probability under shorter T-hoff. Furthermore, capabilities of parallel acquirement of three-dimensional laser point cloud and two-dimensional photon count images are also demonstrated, highlights the superiorities of this multi-TDC scheme in both active and passive imaging under strong background interference.

Objective The high sensitivity characteristics of InGaAs avalanche focal planes operating in Geiger mode play a critical role in the three-dimensional imaging of extremely weak and distant near-infrared laser targets. Compared to traditional two-dimensional imaging technologies, laser-based three-dimensional imaging provides distinct advantages for acquiring and identifying remote sensing target information. This technology enables the extraction of significant characteristic data from targets and can effectively detect and recognize targets within complex backgrounds. Photon detection efficiency (PDE) serves as a key engineering performance metric for detector devices. To enhance switching speed, reduce power consumption, and minimize voltage loss, current devices frequently adopt a double-diffused PN junction structure. Notably, the pixels of the double-diffused PN junction structure differ from those of traditional PIN integrating detectors in terms of layout area, as they occupy a larger footprint. Consequently, for pixels of equivalent size, the effective photosensitive area percentage of detectors with a double-diffused PN junction structure is reduced. This reduction negatively impacts the device's effective fill factor and PDE. In this study, we investigated the design parameters of microlens arrays, surface topography, high-precision optical registration, and low-temperature deformation control, ultimately developing a packaged component for the focal plane tube shell that integrated a microlens array. We aim to improve the performance of InGaAs avalanche focal plane photon detectors and establish a robust foundation for their engineering applications. Methods Firstly, based on the focal plane characteristics of the InGaAs detector, an optical system incorporating microlenses with varying thicknesses was designed. We evaluated the deformation and stress experienced by these microlenses at low temperatures. Subsequently, we introduced the structure of a packaged InGaAs detector component that integrated a micro-lens array. The surface topography, curvature, and focal length of the fabricated microlens array were characterized using a precisely adjustable charge-coupled device (CCD) camera and a step instrument. The bonding process for coupling the microlens array with the focal plane was investigated to determine the deformation and root mean square (RMS) values of the microlens under various bonding conditions. The packaged component of the focal plane was finalized through a high-precision optical registration process involving the microlens array and the infrared focal plane. Furthermore, we compared the PDEs of the components before and after the integration of the microlens. Finally, a series of aerospace-grade environmental tests were conducted on the assembled InGaAs detector with integrated microlens arrays. Results and Discussions The results demonstrate that as the thickness of the microlens increases, the field of view angle of the system decreases, while both the lens radius and focal length increase (Table 1). Due to the constraint imposed by the chip, a thinner microlens exhibits reduced deformation and an elevated equivalent stress value (Fig. 2). The InGaAs detector component, which integrates the microlens, adopts a ceramic tube packaging configuration (Fig. 3). Characterizations of the microlens topography, curvature, and focal length indicate that the surface of the fabricated microlens array is smooth, with a radius error of 5.63% relative to the design value and a focal length error of 7.2% (Fig. 4 and Fig. 6). Among the five adhesive bonding processes used for coupling the microlens array with the focal plane, the fourth glue coating process yields the smallest microlens deformation and RMS value. At this point, the RMS value of the lens array is measured at 0.102 mu m, signifying an enhancement in the surface profile of the lens array (Fig. 7). Furthermore, through high-precision optical alignment between the microlens array and the infrared focal plane, the centering accuracy deviation between the focal plane and the microlens array is maintained within +/- 3 mu m, resulting in an increase in the average PDE of the detector from 27.21% to 41.66% (Fig. 10). The packaged component successfully passes a series of aerospace-grade environmental tests (Fig. 11). Conclusions We report on the design and development of an InGaAs focal plane component integrated with a microlens array, along with a comprehensive investigation into the design, fabrication, testing, and coupling of the microlens array. A packaged component featuring integrated microlenses is successfully developed by leveraging key technologies such as high-precision optical alignment between the microlens array and the infrared focal plane, low-temperature glue control technology with minimal deformation, and low-temperature deformation control for the microlens array. The alignment accuracy deviation between the focal plane and the microlens array is controlled within +/- 3 mu m, leading to a substantial improvement in the PDE of the InGaAs focal plane component, increasing from 27.21% to 41.66%. These findings provide significant reference for advancing the engineering application of InGaAs avalanche focal plane components.

Performances of In0.75 Ga0.25 As focal plane arrays (FPAs) with an extended cutoff wavelength of 2.2 mu m are remarkably improved by largely increasing the overshooting composition of the linearly-grading InxAl1-x As buffer layer. Zinc-diffused planar 640x488 FPAs with a pixel pitch of 23 mu m are fabricated on both the regular and the large overshooting epi-wafers with x=0.77 and x=0.85 for the end compositions of the linearly-grading InxAl1-x As, respectively. An order of magnitude lower dark current density of 1.1x10-10 A/cm(2) is achieved at 150 K for the large overshooting FPAs when comparing with 2.1x10-9 A/cm(2) for the regular FPAs. Suppressed dark signal and dark noise voltages are observed simultaneously over the measured whole integration time range. Moreover, the measured non-uniformity of the light response signal voltage drastically dropped from 16.4% to 2.9% while the peak detectivity substantially jumped from 7.1x10(12) to 1.8x10(13 )cmHz( 1/2) W-1. A signal to noise ratio enhanced laboratory imaging demonstration is also provided. These results suggest the large overshooting epitaxial technology can serve as a highly viable route for the lattice-mismatched InxGa1-x As FPAs towards further performance enhancement.

In this work, the performance of a lattice-mismatched metamorphic In0.83Ga0.17As/InP photodetector with an AlGaAsSb quaternary barrier layer is studied by simulation and compared with that of the photodetector without the barrier layer. By selecting proper elemental compositions, high conduction band offset and zero valence band offset can be obtained. The position and structural parameters of the barrier are analyzed and optimized based on the analysis of energy-band diagram, dark current, quantum efficiency and detectivity at the temperature of 200 K. By placing the barrier at the edge of the depletion region within the absorption layer, and taking the thickness of 0.1 mu m, the dark current has about two orders of magnitude reduction and the detectivity has about one order of magnitude increase without compromising quantum efficiency, compared to those without the barrier layer. The results demonstrate that the AlGaAsSb quaternary alloy can serve as an effective unipolar barrier for the In0.83Ga0.17As/InP photodetector to greatly enhance its performance at 200 K. The barrier structure could be well applied to InGaAs/InP photodetectors for extended short wavelength infrared range.

The application of InGaAs focal plane arrays (FPAs) requires high density and small pixel pitch. However, as the pixel pitch decreases, the pixel coupling becomes stronger. By fabricating 5 mu m pitch InGaAs arrays with different scales, the pixel coupling effects in high-density InGaAs arrays were studied. Innovatively, matrix equations were introduced to describe the contributions of dark current from each part, and a mathematical model of pixel coupling was constructed, and the contributions of the dark current resulting from the coupling effects were quantitatively analyzed. The results indicated that at a bias voltage of -0.1 V, reverse-biased pixels in the array can reduce the dark current of adjacent reverse-biased pixels by 21.39% of the pixel''s initial dark current. In contrast, zero-biased pixels can increase the dark current of adjacent reverse-biased pixels by 219.42%. Based on this high-density focal plane pixel coupling model, the impact rules of pixel coupling on dark current have been summarized, providing new insights for dark current research in high-density InGaAs focal plane arrays.

A planar In0.53Ga0.47As avalanche photodiode (APD) with a triple-stage cascaded InAlAs/InAlGaAs multiplication structure is designed and fabricated. Double zinc-diffusion p-n junction is formed to suppress the perimeter premature breakdown. A low dark current of 4.8 nA at around breakdown voltage is obtained at room temperature for a 40 mu m diameter device with a maximum gain-bandwidth product of 216 GHz. The E-field profile is modulated by doping of a thin In0.52Al0.48As subcharge layer within each multiplication stage. Moreover, electron and hole potential wells are also introduced by the In0.52Al0.24Ga0.24As layers within each stage. The measured hole-initiated maximum gain factor and excess noise factor are 77 and F=6.3 at 200 K, respectively, which well agree with the predicted results base on the dead-space multiplication theory. These results indicate the planar multi-stage multiplication regime is a viable route for fabrication of APDs towards low excess noise while maintaining of a low dark current.