Short-wave infrared InGaAs photodetectors and focal plane arrays

In this article, unique spectral features of short-wave infrared band of 1 μm–3 μm, and various applications related to the photodetectors and focal plane arrays in this band, are introduced briefly. In addition, the different material systems for the devices in this band are outlined. Based on the background, the development of lattice-matched and wavelengthextended InGaAs photodetectors and focal plane arrays, including our continuous efforts in this field, are reviewed. These devices are concentrated on the applications in spectral sensing and imaging, exclusive of optical fiber communication.     

Recent infrared detector technologies,applications, trends and development of HgCdTe based cooled infrared focal plane arrays and their characterization

Infrared thermal imaging, using cooled and uncooled detectors, is continuously gaining attention because of its wide military and civilian applications. Futuristic requirements of high temperature operation, multispectral imaging, lower cost, higher resolution (using pixels) etc. are driving continuous developments in the field. Although there are good reviews in the literature by Rogalski [1–4], Martyniuk et al. [5] and Rogalski et al. [6] on various types of infrared detectors and technologies, this paper focuses on some of the important recent trends and diverse applications in this field and discusses some important fundamentals of these detectors.     

Towards dualband megapixel QWIP focal plane arrays

Mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) 1024 × 1024 pixel quantum well infrared photodetector (QWIP) focal planes have been demonstrated with excellent imaging performance. The MWIR QWIP detector array has demonstrated a noise equivalent differential temperature (NEΔT) of 17 mK at a 95 K operating temperature with f/2.5 optics at 300 K background and the LWIR detector array has demonstrated a NEΔT of 13 mK at a 70 K operating temperature with the same optical and background conditions as the MWIR detector array after the subtraction of system noise. Both MWIR and LWIR focal planes have shown background limited performance (BLIP) at 90 K and 70 K operating temperatures respectively, with similar optical and background conditions. In addition, we have demonstrated MWIR and LWIR pixel co-registered simultaneously readable dualband QWIP focal plane arrays. In this paper, we will discuss the performance in terms of quantum efficiency, NEΔT, uniformity, operability, and modulation transfer functions of the 1024 × 1024 pixel arrays and the progress of dualband QWIP focal plane array development work.     

Resonant detectors and focal plane arrays for infrared detection

We are developing resonator-QWIPs for narrowband and broadband long wavelength infrared detection. Detector pixels with 25 μm and 30 μm pitches were hybridized to fanout circuits and readout integrated electronics for radiometric measurements. With a low to moderate doping of 0.2–0.5 × 10¹⁸ cm⁻³ and a thin active layer thickness of 0.6–1.3 μm, we achieved a quantum efficiency between 25 and 37% and a conversion efficiency between of 15 and 20%. The temperature at which photocurrent equals dark current is about 65 K under F/2 optics for a cutoff wavelength up to 11 μm. The NEΔT of the FPAs is estimated to be 20 mK at 2 ms integration time and 60 K operating temperature. This good performance confirms the advantages of the resonator-QWIP approach.     

红外焦平面阵列非线性校正曲线测量方法

针对红外焦平面阵列强度响应的非线性失真现象,本文提出了一种基于单波长激光器测定红外焦平面阵列非线性校正曲线的方法,设计出用于测量的实验装置,并通过实验研究获得了实测的非线性校正曲线。结果表明,该方法规避了红外焦平面阵列光谱响应不均匀性的影响,满足了装置器件在工程技术中通用性和实用性的需要,在简单易行的同时保证了较高的测量精度。     

Mid-wavelength type II InAs/GaSb superlattice infrared focal plane arrays

We have demonstrated 384 × 288 pixels mid-wavelength infrared focal plane arrays (FPA) using type II InAs/GaSb superlattice (T2SL) photodetectors with pitch of 25 μm. Two p-i-n T2SL samples were grown by molecular beam epitaxy with both GaAs-like and InSb-like interface. The diode chips were realized by pixel isolation with both dry etching and wet etching method, and passivation with SiN_x layer. The device one with 50% cutoff wavelength of 4.1 μm shows NETD ∼ 18 mK from 77 K to 100 K. The NETD of the other device with 50% cutoff wavelength at 5.6 μm is 10 mK at 77 K. Finally, the T2SL FPA shows high quality imaging capability at the temperature ranging from 80 K to 100 K which demonstrates the devices’ good temperature performance.     

Comparison of NETD performance of staring and partial-scanning infrared focal plane arrays

The NETD performance of two main configurations are compared: a staring matrix and a partial-scanning system in which a number of vectors, equally-spaced along the image width, are scanning in parallel with a smaller amplitude. The comparison is systematically derived and is valid for both the hybrid and monolithic approaches. The derivation leads to an optimal design procedure for the partial-scanning configuration, based on the optimization of the direct integration time. Several numerical examples relevant to current technologies are presented. In cases characterized by high photon flux levels or 2-D cold shield with low efficiency, the partial-scanning configuration may yield better NETD values compared to a staring system. In addition, it usually has a better spatial resolution and hence may result in superior MRTD performance.     

Fabrication of type-II InAs/GaSb superlattice long-wavelength infrared focal plane arrays

In this paper, we present an InAs/GaSb type-II superlattice (SL) with the M-structure for the fabrication of a long-wavelength (10 μm range) infrared (LWIR) focal plane arrays (FPA), which are grown by molecular beam epitaxy (MBE). The M-structure is named for the shape of the band alignment while the AlSb layer is inserted into the GaSb layer of InAs/GaSb SL. A 320 × 256 LWIR FPA has been fabricated with low surface leakage and high R₀A product of FPA pixels by using anodic sulfide and SiO₂ physical passivation. Experiment results show that the devices passivated with anodic sulfide obviously have higher R₀A than the un-sulphurized one. The 50% cutoff wavelength of the LWIR FPA is 9.1 μm, and the R₀A is 224 Ω cm² with the average detectivity of 2.3 × 10¹⁰ cm Hz^1/2 W⁻¹.     

基于1.5GHz多次谐波超短脉冲门控InGaAs/InP雪崩光电二极管的近红外单光子探测技术研究

提出了一种高速门控盖格模式的铟镓砷/铟磷雪崩光电二极管(InGaAs/InP APD)单光子探测技术。将1.5GHz多次谐波超短脉冲加载到InGaAs/InP APD上,盖革模式下的光生雪崩信号埋藏在短脉冲充放电形成的噪声中,采用700MHz低通滤波器实现了50.6dB的噪声抑制比,有效地提取出了雪崩信号。通过半导体制冷,使InGaAs/InP APD工作在-30℃,1.5GHz短脉冲驱动下的InGaAs/InP APD在1550nm的探测效率为35%,暗计数率为每门6.4×10-5,超过了单纯使用1.5GHz正弦门的探测性能,而且在15%的探测效率下,2.7ns后发生后脉冲的概率仅为每门6.0×10-5。     

Theoretical analysis and experimental application of CDS CMOS integrated circuit for uncooled infrared focal plane arrays

In this paper, a typical correlated double sampling (CDS) complementary metal oxide semiconductor (CMOS) circuit for uncooled infrared focal plane array (IRFPA) is theoretically analyzed, the key factor of CDS CMOS integrated circuit is pointed out, and a new CDS integrated circuit which is high correlative for low-frequency noise is applied in an experimental readout chip for uncooled IRFPA. Theoretical analysis indicates that the sample transfer function of a noise source acted on by CDS processing is related to noise frequency and sampling time interval and the key factor of CDS circuit for reducing or eliminating noise in readout integrated circuit is the sampling time interval. The experimental readout chip with high noise-correlative CDS integrated circuit is fabricated to verify the theoretical analysis, which can be applied to uncooled IRFPAs.     

Readout circuit with dual switching mode design for infrared focal plane arrays

The paper proposes a readout circuit architecture with adjustable integration time for dual-band infrared detectors. The readout circuit uses direct injection to be combined with a capacitive trans-impedance amplifier. The amplifier is sharing between two pixels to reduce the complexity of the readout circuit. The proposed device reduces power consumption and area overhead compared to traditional structures. An experimental chip was fabricated using the TSMC 0.35 μm 2P4 M 5 V process. The resulting unit pixel layout area is 40 μm × 40 μm with input photocurrent ranging from 0.11 pA to 50 nA. CTIA mode is applicable from 0.11 pA to 10 nA, while DI mode is applicable from 3.3 pA to 50 nA. The maximum operating frequency of the chip are 4 MHz. The CTIA output swing is 1.2 V, the DI output swing is 2 V. The signal to noise ratio of the readout circuit is 65 dB and power consumption is less than 9.6 mW.     

Low-frequency noise characteristics of InGaAs quantum-dot infrared photodetector structures grown by atomic layer molecular-beam epitaxy

Optical and electrical characteristics of n–i–n InGaAs/GaAs quantum-dot (QD) infrared photodetectors are reported. In particular, the low-frequency excess electrical noise is measured at room temperature and analyzed in conjunction with the optical properties of the structure. The three stackings of QD were formed by atomic layer molecular-beam epitaxy and highly Si-doped, and AlGaAs current-blocking layer was also included to reduce the dark current. The power-dependent photoluminescence (PL) spectra at 300 K indicates that there are at least three confined states in the QD. The photo-current was observed only at low temperatures (10 K) at wavelengths between 3 and 9 μm with three peaks. The dark current was relatively large and asymmetric at low temperatures. At room temperature the dark current was symmetric and ohmic. The 1/f-like low-frequency noise spectral density exhibited an almost quadratic current dependence giving a large value of the Hooge parameter of the order of unity. The relatively low-growth temperature for the AlGaAs current blocking layer and the high doping at the quantum dots seem to generate a considerable amount of defects and result in low-temperature photodetection and a large low-frequency noise density.     

Fast iterative adaptive nonuniformity correction with gradient minimization for infrared focal plane arrays

A fast scene-based nonuniformity correction algorithm is proposed for fixed-pattern noise removal in infrared focal plane array imagery. Based on minimization of L0 gradient of the estimated irradiance, the correction function is optimized through correction parameters estimation via iterative optimization strategy. When applied to different real IR data, the proposed method provides enhanced results with good visual effect, making a good balance between nonuniformity correction and details preservation. Comparing with other excellent approaches, this algorithm can accurately estimate the irradiance rapidly with fewer ghosting artifacts.     

InGaAs/InAlAs多量子阱脊形波导及定向耦合器光波特性准矢量分析

提出了一种基于级数展开的三维准矢量束传播法(SE-QV-BPM)用以分析由InGaAs/InAlAs多量子阱构成的脊形光波导及定向耦合器.结果表明，刻蚀深度相同时，TM模比TE模在水平方向限制强，且TM模的模场在波导角上出现畸变；波导间距相同时，定向耦合器TM波的耦合长度大于TE波的耦合长度，对偏振态敏感.分析获得了浅/深刻脊形光波导承载的准矢量TE/TM基模、定向耦合器承载的TE/TM偶/奇模的模场分布及其有效折射率，模拟了光场在定向耦合器中的传输演变情况.另外，SE-QV-BPM导出矩阵小，计算效率高 关键词： 级数展开 准矢量束传播法 多量子阱 InGaAs/InAlAs     

Design of spectral crosstalk suppressing structure in two-color HgCdTe infrared focal plane arrays detector

Spectral crosstalk suppressing design of two-color HgCdTe medium-wave/long-wave (MW/LW) \(\hbox {n}^{+}\) – \(\hbox {p}_{1}\) – \(\hbox {P}_{2}\) – \(\hbox {P}_{3}\) – \(\hbox {N}^{+}\) infrared focal plane arrays (IRFPAs) detector functioning in simultaneous mode is carried out in this study, using Crosslight Technology Computer Aided Design (TCAD) software. A compositional barrier of \(\hbox {P}_{2}\) -region sandwiched between LW absorption layer of \(\hbox {p}_{1}\) -region and MW absorption layer of \(\hbox {P}_{3}\) -region is designed to suppress spectral crosstalk. MW-to-LW crosstalk can be significantly suppressed to 2.1 % while LW-to-MW crosstalk can be maintained less than 1 % by integrating an optimized compositional barrier.     

Study on thermal effects of InSb infrared focal plane arrays irradiated by pulsed laser

To learn thermal effects of InSb infrared focal plane arrays (IRFPAs) detector irradiated by pulsed laser, basing on ANSYS software, and considering temperature dependent thermal parameters of InSb, a three dimensional temperature field analysis model of InSb IRFPAs detector by 1064 nm Gauss laser irradiation is built. The characteristics of temperature rise and temperature distribution in InSb IRFPAs detector are studied. The results show that the maximum temperature always occurs in InSb chip, locating at the top layer of InSb IRFPAs detector, the temperature rises in each layer are different, and the temperature distribution in InSb IRFPAs detector is quite different from that in single-layer material. The temperature distribution of InSb chip in InSb IRFPAs reduces from center to outside, while it shows not a smooth decrease, but a concentric-ringed ripple decrease with non-consecutive high temperature extremum regions. The temperature distribution patterns in underfill, Si readout integrated circuits are similar to that in InSb chip, but the discontinuous high temperature areas in InSb chip, underfill locate at the regions between indium bumps, and the discontinuous high temperature areas in Si readout integrated circuits locate at the contact area with indium bumps. This different temperature distribution phenomenon in each material is mainly due to its multi-layer architecture and quite different thermal properties of the middle layer, which is an interlacing layout of underfill and indium bumps. Besides, the influences of indium bump structure size on the temperature rise are also discussed. All these results qualitatively reflect the disciplines of temperature rise in InSb IRFPAs detector, providing a theory support for thermal analysis of detectors irradiated by laser.     

Improvement in adaptive nonuniformity correction method with nonlinear model for infrared focal plane arrays

The scene adaptive nonuniformity correction (NUC) technique is commonly used to decrease the fixed pattern noise (FPN) in infrared focal plane arrays (IRFPA). However, the correction precision of existing scene adaptive NUC methods is reduced by the nonlinear response of IRFPA detectors seriously. In this paper, an improved scene adaptive NUC method that employs “S”-curve model to approximate the detector response is presented. The performance of the proposed method is tested with real infrared video sequence, and the experimental results validate that our method can promote the correction precision considerably.     

Assessment of HgCdTe photodiodes and quantum well infrared photoconductors for long wavelength focal plane arrays

Recent trends in infrared detectors are towards large, electronically addressed two-dimensional arrays. In the long wavelength infrared (LWIR) spectral range HgCdTe focal plane arrays (FPAs) occupy a dominant position. However, the slow progress in the development of large LWIR photovoltaic HgCdTe infrared imaging arrays and the rapid achievements of novel semiconductor heterostructure systems have made it necessary to foresee the future development of different material technologies in fabrication large FPAs. Among the competing technologies in LWIR are the quantum well infrared photoconductors (QWIPs) based on lattice matched GaAs/AlGaAs and strained layer InGaAs/AlGaAs material systems. This paper compares the technical merits of two IR detector arrays technologies; photovoltaic HgCdTe and QWIPs. It is clearly shown that LWIR QWIP cannot compete with HgCdTe photodiode as the single device especially at higher temperature operation (>70 K) due to fundamental limitations associated with intersubband transitions. However, the advantage of HgCdTe is less distinct in temperature range below 50 K due to problems involved in HgCdTe material (p-type doping, Shockley–Read recombination, trap-assisted tunnelling, surface and interface instabilities). Even though the QWIP is a photoconductor, several of its properties such as high impedance, fast response time, long integration time, and low power consumption, well satisfy the requirements of fabrication of large FPAs. Due to the high material quality at low temperature, QWIP has potential advantages over HgCdTe for very LWIR (VLWIR) FPA applications in terms of the array size, uniformity, yield and cost of the systems.     

Numerical simulation of the modulation transfer function in planar InGaAs dense arrays

Three-dimensional simulation methodology has been used to evaluate the performance of lattice matched InGaAs/InP double layer planar heterointerface detector arrays. The device characteristics under optical illumination and dark conditions have been computed. The modulation transfer function (MTF) profiles have been calculated with varying device geometries and carrier dynamics. It is found that the p well diffusion radius and minority carrier recombination play important roles in the MTF behaviors of dense arrays. Moderate p well diffusion dimension should be used to balance the device performances between the dark current and MTF profile. Moreover, better MTF characteristic under low light condition can be achieved with higher quality material which has longer recombination lifetime. The influences of underlying mechanisms including photon generated carriers diffusion and carrier recombination processes have been discussed. These simulation methods and results should provide a useful tool for the evaluation and improvement of imaging power of InGaAs focal plane arrays.     

无基底焦平面阵列的红外成像性能分析

利用提出的光学读出非制冷红外成像系统,先后制作了单元尺寸各不相同的单层膜无基底焦平面阵列(focal plane array,FPA),获得了室温物体的热图像.分析发现,当FPA的单元尺寸从200μm逐渐减小到60μm时,基于恒温基底模型的理论响应与实验结果的偏差逐渐增大.通过有限元分析方法,模拟分析了不同尺寸的微梁单元在无基底FPA中的热学行为,发现了当单元尺寸逐渐减小时恒温基底模型偏差逐渐增大的原因,即无基底FPA的支撑框架不满足恒温基底条件,受热辐射后支撑框架的温升从基底上抬高了单元的温升.论文还分 关键词： 光学读出 非制冷红外成像 焦平面阵列 无基底