中/长波切换工作模式的双色量子阱红外焦平面研制

报道了中/长波切换工作模式的双色量子阱红外焦平面研制。通过特殊设计的器件和读出电路结构,获得了可对中波波段和长波波段选择的切换架构。突破了双色量子阱材料、器件以及读出电路等关键技术,研制出384288规模、25 m中心距双色量子阱红外焦平面探测器。在70 K条件下器件性能优良,噪声等效温差为28 mK(中波)和30 mK(长波),响应峰值波长分别为5.1 m(中波)和8.5 m(长波)。室温目标红外成像演示了探测器的双色探测功能。     

The HgCdTe electron avalanche photodiode

Electron injection avalanche photodiodes in short-wave infrared (SWIR) to long-wave infrared (LWIR) HgCdTe show gain and excess noise properties indicative of a single ionizing carrier gain process. The result is an electron avalanche photodiode (EAPD) with “ideal” APD characteristics including near noiseless gain. This paper reports results obtained on long-, mid-, and short-wave cutoff infrared Hg_1−xCd_xTe EAPDs (10 μm, 5 μm, and 2.2 μm) that use a cylindrical “p-around-n” front side illuminated n+/n-/p geometry that favors electron injection into the gain region. These devices are characterized by a uniform, exponential, gain voltage characteristic that is consistent with a hole-to-electron ionization coefficient ratio, k=α_h/α_e, of zero. Gains of greater than 1,000 have been measured in MWIR EAPDS without any sign of avalanche breakdown. Excess noise measurements on midwave infrared (MWIR) and SWIR EAPDs show a gain independent excess noise factor at high gains that has a limiting value less than 2. At 77 K, 4.3-μm cutoff devices show excess noise factors of close to unity out to gains of 1,000. A noise equivalent input of 7.5 photons at a 10-ns pulsed signal gain of 964 measured on an MWIR APD at 77 K provides an indication of the capability of this new device. The excess noise factor at room temperature on SWIR EAPDs, while still consistent with the k=0 operation, approaches a gain independent limiting value of just under 2 because of electron-phonon interactions expected at room temperature. The k=0 operation is explained by the band structure of the HgCdTe. Monte Carlo modeling based on the band structure and scattering models for HgCdTe predict the measured gain and excess noise behavior.     

宽波段DMD动态红外景象仿真器投影光学系统设计

宽波段红外景象仿真器可用于内场评价和验证中波/长波红外双波段成像仪。详细介绍了基于数字微镜器件(DMD)的动态红外景象仿真器的组成和工作原理。重点介绍了覆盖中波和长波红外的宽波段红外投影光学系统的指标要求、设计思想和设计结果。基于离轴三反射镜系统设计的系统,具有无色差、适用波段宽、相对孔径大、结构较紧凑、成像质量好等优点。根据待测设备要求,设计了一款口径100、相对孔径F/2.84、全面视场角4.4°、成像质量接近于衍射极限的宽波段投影光学系统。     

A monolithic dual-band HgCdTe infrared detector structure

A monolithic HgCdTe photoconductive device structure is presented that is suitable for dual-band optically registered infrared photodetection in the two atmospheric transmission windows of 3-5 μm and 8-12 μm, which correspond to the mid-wave and long-wave infrared bands; MWIR and LWIR, respectively. The proposed structure employs a wider bandgap isolating layer between the two photosensitive layers such that an effective electrical barrier is formed thus prohibiting carrier transport between the two infrared absorbing layers of different cutoff wavelengths. The technology is demonstrated using a mature HgCdTe photoconductive device fabrication process. The resulting detectors have an MWIR cutoff of 5.0 μm, and LWIR cutoff of 10.5 μm     

Localization of excited carriers in organometallic vapor-phase epitaxial grown Zn<Subscript>x</Subscript>Cd<Subscript>1−x</Subscript>Se epilayers with partial existence of lateral compositionally modulated superlattice

The structural and optical properties of organometallic vapor-phase epitaxial (OMVPE) grown Zn_xCd_1−xSe epilayers on the (001) InP substrate were studied by transmission electron microscopy (TEM) and photoluminescence (PL). The TEM results showed the spontaneous formation of compositionally modulated (CM) superlattices along the [110] direction with a period of ∼10–20 nm at some places in the epilayer. In the PL measurements, we found an anomalous red shift of PL with a decrease in temperature (from 170 K to 100 K) and a large blue shift up to 40 meV with an increase in excitation power. We suggested that the anomalous red shift of PL is caused by a localization of photo-excited carriers from places containing a normal random alloy to places containing a CM superlattice, which has a narrower bandgap, and the large blue shift is caused by a saturation of energy states in the CM superlattice under high excitation. The narrower bandgap of the CM superlattice is supported by a polarized PL study, where the low energy part of PL is strongly polarized along the [ ] direction, is consistent with the reduced symmetry of a CM superlattice. A two-level model was proposed to quantitatively account for the experimental observations.     

VSWIR to VLWIR MBE grown HgCdTe material and detectors for remote sensing applications

The molecular beam epitaxy (MBE) growth technology is inherently flexible in its ability to change the Hg_1−xCd_xTe material’s bandgap within a growth run and from growth run to growth run. This bandgap engineering flexibility permits tailoring the device architecture to the various specific requirements. Material with active layer x values ranging from ∼0.198 to 0.570 have been grown and processed into detectors. This wide range in x values is perfectly suited for remote sensing applications, specifically the National Polar Orbiting Environmental Satellite System (NPOESS) program that requires imaging in a multitude of infrared spectral bands, ranging from the 1.58 to 1.64 μm VSWIR (very short wave infrared) band to the 11.5 to 12.5 μm LWIR (longwave infrared) band and beyond. These diverse spectral bands require high performance detectors, operating at two temperatures; detectors for the VSWIR band operate near room temperature while the SWIR, MWIR (mid wave infra red), LWIR and VLWIR (very long wave infrared) detectors operate near 100K, because of constraints imposed by the cooler for the NPOESS program. This paper uses material parameters to calculate theoretical detector performance for a range of x values. This theoretical detector performance is compared with median measured detector optical and electrical data. Measured detector optical and electrical data, combined with noise model estimates of ROIC performance are used to calculate signal to noise ratio (SNR), for each spectral band. The SNR are compared with respect to the meteorological NPOESS system derived focal plane. The derived system focal plane requirements for NPOESS are met in all the spectral bands.     

Uncooled InAs-GaSb type-II infrared detectors grown on GaAssubstrates for the 8-12-μm atmospheric window

We report on the growth and characterization of type-II infrared detectors with an InAs-GaSb superlattice active layer for the 8-12-μm atmospheric window at 300 K. The material was grown by molecular beam epitaxy on semi-insulating GaAs substrates. Photoconductive detectors fabricated from the superlattices showed 80% cutoff at about 12 μm at room temperature. The responsivity of the device is about 2 mA/W with a 1-V bias (E=5 V/cm) and the maximum measured detectivity of the device is 1.3×10⁸ cm.Hz^1/2/W at 11 μm at room temperature. The detector shows very weak temperature sensitivity. Also, the extracted effective carrier lifetime, τ=26 ns, is an order of magnitude longer than the carrier lifetime in HgCdTe with similar bandgap and carrier concentration     

SiGe/Si异质结的基本特性及其探测器的应用前景

综述了SiGe应变层的基本性质,包括SiGe应变层的临界厚度与超晶格的稳定性、带隙和能带变化、折射率 增量以及等离子色散效应。总结了材料生长中释放应力的两种形式,包括位错和表面起伏。最后介绍了SiGe/Si应变量 子阱光电探测器和红外焦平面阵列探测器的进展及其应用前景。     

Tilted superlattice composition profile determined by photoluminescence and thermal disordering

The composition profile of an (AlAs)_1/2(GaAs)_1/2 tilted superlattice is characterized for the first time. The tilted superlattice sample is thermally disordered, and the energy of the direct band gap photoluminescence peak is measured as a function of increasing layer interdiffusion. The shift in the photoluminescence peak energy after completely disordering the tilted superlattice is 39 meV. A theoretical model is used to simulate the change in band gap as a function of layer interdiffusion for several composition profiles. The profile that gives the best fit to the experimental data is chosen. The tilted superlattice composition profile is found to be sinusoidal, varying from Al_0.40Ga_0.60As to Al_0.60Ga_0.40As.     

Demonstration and Performance Assessment of Large Format InP–InGaAsP Quantum-Well Infrared Photodetector Focal Plane Array

There have been various studies showing that InP-InGaAs quantum-well infrared photodetectors (QWIPs) are potential alternatives to AlGaAs-GaAs QWIPs in the long wavelength infrared (LWIR) band, especially for applications requiring high responsivity. Being on InP substrate, this material system also offers lattice matched mid-wavelength infrared (MWIR)/LWIR dual band QWIP stack when it is used with the AlInAs-InGaAs system. It is desirable to extend the cut-off wavelength of InP based LWIR QWIPs to , which can be accomplished by replacing the QW material with InGaAsP. In this paper, we report the first InP-InGaAsP QWIP focal plane array (FPA). The 640 512 FPA displayed remarkably low noise equivalent temperature difference (NETD) with very short integration times (46 mK at 66 K with and f/1.5 optics). The results show that these QWIPs can be operated with high responsivity (1 A/W) while offering bias adjustable gain in a wide range where the detectivity is almost constant at a reasonably high level.     

Accurate measurement of composition, carrier concentration, and photoconductive lifetime in Hg1−xCdxTe grown by molecular beam epitaxy

Variable magnetic field Hall and transient photoconductance lifetime measurements were performed on a series of undoped, In-doped, and As-doped HgCdTe samples grown by molecular beam epitaxy and metalorganic chemical vapor deposition. Temperature variation and, in the case of Hall, magnetic-field variation are needed to give a more complete picture of the mechanisms that control lifetimes in HgCdTe samples. Recent predictions of recombination lifetimes from full band structure calculations were compared to experimental lifetimes at various doping levels at long-wave infrared (LWIR) and mid-wave infrared (MWIR) compositions. For n-type material, lifetimes from low doping levels fall well below the predictions, implying that Shockley-Read-Hall (SRH) recombination is still dominant. MWIR samples have a lifetime that increases somewhat with carrier concentration, suggesting that In doping passivates the SRH defects for that composition. Lifetimes in p-type MWIR material appear to be well-explained by recent theoretical calculations. In p-type material, trapping states may be introduced during the incorporation and activation of As, since some samples with unusually long lifetimes had a distinctly different type of temperature dependence.     

HgCdTe focal plane arrays for dual-color mid- and long-wavelength infrared detection

Raytheon Vision Systems (RVS, Goleta, CA) in collaboration with HRL Laboratories (Malibu, CA) is contributing to the maturation and manufacturing readiness of third-generation, dual-color, HgCdTe infrared staring focal plane arrays (FPAs). This paper will highlight data from the routine growth and fabrication of 256×256 30-μm unit-cell staring FPAs that provide dual-color detection in the mid-wavelength infrared (MWIR) and long wavelength infrared (LWIR) spectral regions. The FPAs configured for MWIR/MWIR, MWIR/LWIR, and LWIR/LWIR detection are used for target identification, signature recognition, and clutter rejection in a wide variety of space and ground-based applications. Optimized triple-layer heterojunction (TLHJ) device designs and molecular beam epitaxy (MBE) growth using in-situ controls has contributed to individual bands in all dual-color FPA configurations exhibiting high operability (>99%) and both performance and FPA functionality comparable to state-of-the-art, single-color technology. The measured spectral cross talk from out-of-band radiation for either band is also typically less than 10%. An FPA architecture based on a single-mesa, single-indium bump, and sequential-mode operation leverages current single-color processes in production while also providing compatibility with existing second-generation technologies.     

Growth and properties of digitally-alloyed AlGaInP by solid source molecular beam epitaxy

Digital alloying using molecular beam epitaxy (MBE) was investigated to produce AlGaInP quaternary alloys for bandgap engineering useful in 600-nm band optoelectronic device applications. Alternating Ga_0.51In_0.49P/Al_0.51In_0.49P periodic layers ranging from 4.4 monolayers (ML) to 22.4 ML were used to generate 4,000-Å-thick (Al_0.5Ga_0.5)_0.51In_0.49P quaternary materials to understand material properties as a function of constituent superlattice layer thickness. High-resolution x-ray diffraction (XRD) analysis exhibited fine satellite peaks for all the samples confirming that digitally-alloyed (Al_0.5Ga_0.5)_0.51In_0.49P preserved high structural quality consistent with cross-sectional transmission electron microscopy (X-TEM) images. Low-temperature photoluminescence (PL) measurements showing a wide span of luminescence energies ～ 170 meV can be obtained from a set of identical composition digitally-alloyed (Al_0.5Ga_0.5)_0.51In_0.49P with different superlattice periods, indicating the bandgap tunability of this approach and its viability for III-P optoelectronic devices grown by MBE.     

High-Performance MWIR/LWIR Dual-Band 640 × 480 HgCdTe/Si FPAs

HgCdTe grown on large-area Si substrates allows for larger array formats and potentially reduced focal-plane array (FPA) cost compared with smaller, more expensive CdZnTe substrates. The goal of this work is to evaluate the use of HgCdTe/Si for mid-wavelength/long-wavelength infrared (MWIR/LWIR) dual-band FPAs. A series of MWIR/LWIR dual-band HgCdTe triple-layer n-P-n heterojunction (TLHJ) device structures were grown by molecular-beam epitaxy (MBE) on 100-mm (211)Si substrates. The wafers showed low macrodefect density (<300 cm⁻²) and was processed into 20-μm-unit-cell 640 × 480 detector arrays which were mated to dual-band readout integrated circuits (ROICs) to produce FPAs. The measured 80-K cutoff wavelengths were 5.5 μm for MWIR and 9.4 μm for LWIR, respectively. The FPAs exhibited high pixel operabilities in each band, with noise equivalent differential temperature (NEDT) operabilities of 99.98% for the MWIR band and 99.6% for the LWIR band demonstrated at 84 K.     

(111)方向的InAs/GaSb超晶格材料电子结构的杂化泛函计算

采用电子密度泛函理论方法计算了一系列（111）方向的InAs/GaSb超晶格的电子结构和能带结构。将杂化泛函的计算结果与普通密度泛函方法的计算结果进行了比较。Heyd-Scuseria-Ernzerhof (HSE)杂化与对固体修正的Perdew-Burke-Ernzerhof (PBE)近似结合的杂化泛函显示了较传统PBE方法和若干其他杂化泛函更符合实验数据的结果。采用该方法研究了InAs/GaSb超晶格的带隙随超晶格周期厚度以及InAs/GaSb比例变化的规律。其结果与以往实验结果符合很好。这些结果表明HSE-PBEsol方法对于估计InAs/GaSb超晶格的电子性质适用。     

机载高光通量双波段成像光谱仪的设计

分析了成像光谱仪常见结构的优缺点并给出了分析过程,对望远镜系统和光谱成像系统结构进行了合理选择,实现了单一成像光谱仪同时覆盖可见近红外(VNIR)和中波红外(MWIR)双波段。根据研究目标要求设计了一个大F数(VNIR波段F/3,MWIR波段F/2)机载双波段成像光谱仪。该光谱仪双通道共用一个同轴平场无遮挡Schwarzschild望远镜,用二向色分束器分开。双通道光谱成像系统均采用同心共轴的Dyson结构,VNIR波段和MWIR波段光谱分辨率分别达到5 nm和15 nm。为使设计的系统结构合理,介绍了光束分离结构和光谱仪的光束折叠方法。设计结果表明:该系统结构简单,效果良好,谱线弯曲分别小于1.2μm和0.5μm,谱带弯曲均小于0.5μm,偏振灵敏度小于4%,适用高光谱分辨率机载双波段成像光谱仪。     

Li4Ti5O12: A Visible‐to‐Infrared Broadband Electrochromic Material for Optical and Thermal Management

Broadband electrochromism from visible to infrared wavelengths is attractive for applications like smart windows, thermal camouflage, and temperature control. In this work, the broadband electrochromic properties of Li₄Ti₅O₁₂ (LTO) and its suitability for infrared camouflage and thermoregulation are investigated. Upon Li⁺ intercalation, LTO changes from a wide bandgap semiconductor to a metal, causing LTO nanoparticles on metal to transition from a super‐broadband optical reflector to a solar absorber and thermal emitter. Large tunabilities of 0.74, 0.68, and 0.30 are observed for the solar reflectance, mid‐wave infrared (MWIR) emittance, and long‐wave infrared (LWIR) emittance, respectively, with a tunability of 0.43 observed for a wavelength of 10 µm. The values exceed, or are comparable to notable performances in the literature. A promising cycling stability is also observed. MWIR and LWIR thermography reveal that the emittance of LTO‐based electrodes can be electrochemically tuned to conceal them amidst their environment. Moreover, under different sky conditions, LTO shows promising solar heating and subambient radiative cooling capabilities depending on the degree of lithiation and device design. The demonstrated capabilities of LTO make electrochromic devices based on LTO highly promising for infrared‐camouflage applications in the defense sector, and for thermoregulation in space and terrestrial environments.     

ZnO/ZnCdO和ZnO/ZnMgO超晶格的子带研究

ZnO是具有3.37 eV的宽禁带半导体材料,近年来引起了众多研究者的兴趣。Zn1-xCdxO和Zn1-xMgxO很好地实现了对ZnO能带的减小和增大。采用较为简单的一维K P势模型结合有效质量理论得到了ZnO/Zn1-xCdxO及ZnO/Zn1-xMgxO多量子阱的能量色散关系,以及子带的MeV跃迁与超晶格带阶、阱垒宽度之间的关系。将该多量子阱应用于太赫兹量子级联激光器(THz QCL)有源区,对粒子数反转和跃迁矩阵进行了相关讨论。     

Large-Format Voltage-Tunable Dual-Band Quantum-Well Infrared Photodetector Focal Plane Array for Third-Generation Thermal Imagers

We report a large-format (640 times 512) voltage- tunable quantum-well (QW) infrared photodetector focal plane array (FPA) for dual-band imaging in the mid- and long-wavelength infrared (MWIR and LWIR) bands. Voltage-tunable spectral response has been achieved through a series connection of eight-well MWIR AlGaAs-InGaAs and 16-well LWIR AlGaAs-GaAs QW stacks grown by molecular beam epitaxy on GaAs substrate. The peak responsivity wavelength of the detectors is shifted from 4.8 to 8.4 mum as the bias is increased within the limit applicable by commercial read-out integrated circuits. The FPA with MWIR and LWIR cutoff wavelengths of 5.1 and 8.9 mum provides noise equivalent temperature differences of 20 and 32 mK (f/1.5) in these bands, respectively. The results are very encouraging for the development of low-cost large-format dual-band MWIR/LWIR FPA technology.     

High-Performance M/LWIR Dual-Band HgCdTe/Si Focal-Plane Arrays

Mercury cadmium telluride (HgCdTe) grown on large-area silicon (Si) substrates allows for larger array formats and potentially reduced focal-plane array (FPA) cost compared with smaller, more expensive cadmium zinc telluride (CdZnTe) substrates. In this work, the use of HgCdTe/Si for mid- wavelength/long-wavelength infrared (M/LWIR) dual-band FPAs is evaluated for tactical applications. A number of M/LWIR dual-band HgCdTe triple-layer n-P-n heterojunction device structures were grown by molecular-beam epitaxy (MBE) on 100-mm (211)Si substrates. Wafers exhibited low macrodefect densities (< 300 cm^?2). Die from these wafers were mated to dual-band readout integrated circuits to produce FPAs. The measured 81-K cutoff wavelengths were 5.1 μm for band 1 (MWIR) and 9.6 μm for band 2 (LWIR). The FPAs exhibited high pixel operability in each band with noise-equivalent differential temperature operability of 99.98% for the MWIR band and 98.7% for the LWIR band at 81 K. The results from this series are compared with M/LWIR FPAs from 2009 to address possible methods for improvement. Results obtained in this work suggest that MBE growth defects and dislocations present in devices are not the limiting factor for detector operability, with regards to infrared detection for tactical applications.