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• An interface control method is proposed to improve the material quality of InAs/InAsSb superlattices. • Mid-wavelength InAs/InAsSb nBn infrared detector with AlAs/AlSb barrier is demonstrated. • Dark current models are used to extract the minority carrier lifetime of InAs/InAsSb superlattices. We report our study to optimize the growth of mid-wavelength InAs/InAsSb nBn infrared detectors through interface control method with AlSb/AlAs superlattices as electron barrier. The dark current model was employed to investigate the dominant dark current mechanism at various operating temperatures. We extracted the minority carrier lifetime of InAs/InAsSb material grown by different interface growth methods. Electrical and optical characterizations indicated superior performance of the device grown by migration-enhanced epitaxy (MEE) with a 3 s As and Sb soak time. With −0.3 V applied bias and 150 K operating temperature, the optimal device shown a dark current density of 8.95 × 10−6 A/cm2 and peak specific detectivity of 7.12 × 1011 cm Hz1/2/W at 3.8 µm. [ABSTRACT FROM AUTHOR]

• Carrier localization in the InAsSb/InSb digital alloy nBn detector varies substantially with spatial location. • This is likely caused by macro-scale nonuniformities in the growth at the mm scale. • These nonuniformities may include sub-monolayer fluctuations in layer thickness and fluctuations in alloy composition. Recently we have demonstrated a novel method of extending the cut-off wavelength of InAsSb nBn detectors, by incorporating a series of monolayers of InSb, which we have termed a digital alloy. In recent work we have shown that while increasing temperature from 15 K to 40 K we observe a 14 meV blue shift of the photoluminescence peak energy and a decrease in minority carrier lifetime. We have hypothesized this effect is due to carrier localization caused by macro-scale fluctuations in layer thickness or alloy composition. Here we study the spatial variation of this effect over the surface of a sample, demonstrating significant variation with position. We discuss implications of this for the carrier localization hypothesis. [ABSTRACT FROM AUTHOR]

Highlights • Delta-doped layers have been utilized to get HgCdTe nBn configurations. • Short (SWIR), medium (MWIR) and long (LWIR) wave infrared bands are examined. • Strong suppression of dark current have been demonstrated. • No degradation in photo response has been observed. • This methodology is especially useful when the carrier lifetime is limited. Abstract Delta-doped layers together with compositionally grading have been utilized to get nBn configurations for the HgCdTe material system in all the short-wave (SWIR), medium-wave (MWIR) and long-wave (LWIR) infrared bands. Shockley Read Hall (SRH), trap-assisted tunneling (TAT), Auger and radiative recombination mechanisms have been included in the analyses and strong suppression of SRH and TAT currents have been demonstrated with the designed structures. This methodology is especially useful when the carrier lifetime is limited due to alternative substrate usage. No degradation in photo-response has been observed as adjusting the valence band offset is quite flexible with the delta-doped nano-layers and the valence band barrier can be completely removed. Calculations have been performed for 1–3 μs lifetime targeting the alternative substrate applications and up to 60 degrees of increase in the operation has been shown to be possible. [ABSTRACT FROM AUTHOR]

Highlights • Theoretical analysis provides simple comparisons of bulk and type-II superlattice infrared absorbers. • Covering short-wavelength infrared to very long wavelength infrared. • Type-II superlattice mid-wavelength infrared detector and focal plane array out-performs InSb. Abstract Advances in bulk III-V semiconductor material such as InGaAsSb and metamorphic InAsSb, as well as in a variety of type-II superlattices such as InGaAs/GaAsSb, InAs/GaSb, and InAs/InAsSb, have provided continuously adjustable cutoff wavelength coverage from the short to the very long wavelength infrared. We perform basic theoretical analysis to provide comparisons of different infrared materials. We also briefly report experimental results on a mid-wavelength InAs/InAsSb type-II superlattice unipolar barrier infrared detector and a focal plane array with significantly higher operating temperature than InSb. [ABSTRACT FROM AUTHOR]

Highlights • Dark-current degradation in nBn detectors under proton irradiation re-investigated. • Previously published work neglected irradiation-induced doping density increase. • New results describe varying power-law between nBn dark-current and proton fluence. Abstract Recent investigations demonstrated that III-V-based nBn infrared detectors typically experience relatively significant performance degradation under 63 MeV proton irradiation due to displacement damage, limiting their viability for certain space-based applications. Additionally, the investigations suggested, based on simplified expressions, that the nBn's diffusion-limited dark-current would transition from a linear-dependence on proton fluence to a square-root-dependence as the minority carrier recombination lifetime decreased and the subsequently decreasing diffusion length became less than the thickness of the detector's quasi-neutral absorbing region. Here, a closer examination of this expected behavior is reported on. Evidence from multiple nBn detector rad-tolerance experiments and simple numerical simulations indicated the behavior of the nBn's diffusion-current under proton irradiation can be more complicated than was previously suggested. For example, in some nBn detectors proton irradiation was observed to increase the doping density of the absorber sufficient to impact the diffusion-current and lessen its power-law-dependence on the proton fluence. This increase was confirmed by analysis of in situ capacitance–voltage measurements on an irradiated nBn detector, which found an n-type carrier addition rate ∼ 140 cm−1. Simulations showed this level of carrier addition can lead to a ∼ 75 % reduction in the expected diffusion-current density for an equivalent dose of 100 krad(Si). Simulations also showed the nBn diffusion-current's instantaneous power law-dependence on proton fluence peaked well below unity and then began approaching −.5 rather than.5, which was suggested by those previous investigation. A high native defect density prior to irradiation and finite surface recombination velocity were both found to reduce the initial power-law dependence and shift its peak position. [ABSTRACT FROM AUTHOR]

Noise Equivalent Difference Temperature (NEΔT) is a standard performance metric for most infrared focal plane array (FPA) systems. The frequency bandwidth and range associated with NEΔT is normally at high frequency and it does not describe the long time noise behavior or the very low frequency noise of the FPA. Very low frequency noise measurement requires data capture that takes longer time duration and sampling interval. This study investigates low frequency noise in QWIP, nBn and LWIR n-type Complementary Barrier Infrared Detector (CBIRD) FPAs. The corner frequencies are extracted from the power spectral density (PSD) as function of frequency. The peak wavelength, quantum efficiency of QWIP detector are 6.2 μm and 2%, respectively. QWIP FPA has a mean NEΔT ∼ 25 mK at an operating temperature of 65 K and an integration time of 16 ms. The mean QWIP PSD plot shows a corner frequency of <0.5 mHz. The nBn FPA with 4 μm cut off and quantum efficiency of 67 % has NEΔT ∼ 15.6 mK at an integration time ∼7.52 ms and an operating temperature of 120 K. The nBn has corner frequency of >50 mHz. Lastly the n-type CBIRD FPA with a 50% cutoff at 8.8 μm and quantum efficiency of ∼50 % has an NEΔT ∼ 18.6 mK at an integration time of 1.86 ms and operating temperature 120 K. The superlattice FPA has a corner frequency ∼10 mHz. The investigation of the tail on the NEΔT histogram reveals that its origin is not accounted for entirely by the high noise current, but also it needs the inclusion of lower responsivity for some pixels. [ABSTRACT FROM AUTHOR]

The low-frequency noise is a ubiquitous phenomenon and the spectral power density of this fluctuation process is inversely proportional to the frequency of the signal. We have measured the 1/f noise of a 640 × 512 pixel quantum well infrared photodetector (QWIP) focal plane array (FPA) with 6.2 μm peak wavelength. Our experimental observations show that this QWIP FPA’s 1/f noise corner frequency is about 0.1 mHz. With this kind of low frequency stability, QWIPs could unveil a new class of infrared applications that have never been imagined before. Furthermore, we present the results from a similar 1/f noise measurement of bulk InAsSb absorber (lattice matched to GaSb substrate) nBn detector array with 4.0 μm cutoff wavelength. [ABSTRACT FROM AUTHOR]

Abstract: When properly employed, unipolar barriers can significantly improve the performance of infrared photodetectors; however, the barriers must be correctly engineered and properly located in the epitaxial structure in order for detectors to function optimally. Unipolar barrier concepts, design, and implementation in several device architectures are discussed. nBn and unipolar barrier photodiodes are demonstrated in the InAs materials system, and the limitations of unipolar barriers are considered. [Copyright &y& Elsevier]

Abstract: Antimony-based materials continue to provide great interest for infrared photodetector and focal plane array imaging applications. Detector architectures include InAs/Ga(In)Sb strained-layer superlattices, which create a type-II band alignment that can be tailored to cover a wide range of the mid- and long-wavelength bands by varying the thickness and composition of the constituent materials, and bulk InAsSb-based XBn barrier designs. These materials can provide desirable detector features such as wider wavelength range, suppression of tunneling currents, improved quantum efficiency, and higher operating temperatures. In order to bring these advantages to market, a reliable manufacturing process must be established on large diameter substrates. We report our latest work on the molecular beam epitaxy growth of Sb-detector epiwafers on 100mm diameter GaSb substrates in a multi-wafer production format. The growth process has been established to address the challenges of these demanding structures, including the large numbers of alternating thin layers and mixed group-V elements. Various characterization techniques demonstrate excellent surface morphology, crystalline structure quality, and optical properties of the epiwafers. The measured wafer-to-wafer consistency and cross-wafer uniformity demonstrate the potential for volume manufacturing. [Copyright &y& Elsevier]

Abstract: This study reports on hydrogenation of InAs nBn photodetectors grown on a lattice mismatched GaAs substrate. The mismatched growth causes increases in dark current by factors of 8–16 (voltage- and temperature-dependent), with respect to similar lattice matched growth. UV hydrogenation of the mismatched nBn’s produced significant decrease in dark current without decreasing the photocurrent. [Copyright &y& Elsevier]