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An analytical model for diffusion-limited detector sensitivity under low-irradiance conditions is derived from carrier continuity equations and verified with Silvaco TCAD drift-diffusion software. The model is used to determine the optimal design parameters for a mid-wave infrared InAs/InAsSb type-II superlattice nBn photodetector for maximum sensitivity under both topside- and backside-illumination conditions. A minimum attainable noise-equivalent irradiance of 4.5 × 1010 photons/cm2 s is found for InAs/InAsSb nBn at 130 K, roughly 2.4× higher than a detector exhibiting Rule 07 dark current density and unity quantum efficiency. A design heuristic, offering a simple and practical approach to designing a high-sensitivity detector, is then developed and performance is found to be comparable to the optimally designed structures. Finally, an evaluation of the impact of each material parameter on noise-equivalent irradiance is performed, revealing that the intrinsic carrier concentration, effective minority carrier lifetime, and absorption coefficient exhibit the largest impacts on sensitivity for diffusion-limited detectors. [ABSTRACT FROM AUTHOR]

An investigation into the effects of 63 MeV proton irradiation on high-sensitivity mid-wave infrared InGaAs/InAsSb nBn devices is performed. Three different structures with various absorber region doping profiles are irradiated and characterized to assess their impact on performance degradation. Minority carrier lifetime is measured using time-resolved photoluminescence and lifetime damage factors are assessed. The majority carrier concentration is determined via capacitance–voltage measurements and dopant introduction rates are calculated. An analysis of dark current density is performed using these material parameters, revealing a reduction in mobility with proton fluence and the emergence of a proton-induced trap energy level. Quantum efficiency is calculated at each proton fluence, and quantum efficiency damage factors show that the graded doping structure exhibits the least reduction of quantum efficiency with dose, attributed to its effective mobility enhancement. Conclusively, detector sensitivity, assessed via shot-noise limited noise-equivalent irradiance, shows that the graded doping structure is the least susceptible to high energy proton irradiation-induced performance degradation. [ABSTRACT FROM AUTHOR]

InAsSbBi nBn photodetectors are demonstrated that are lattice-matched to the underlying GaSb substrate with a 4.32 μm wavelength cutoff at 150 K that is 0.3 μm longer than that of lattice-matched InAsSb at this temperature reflecting a 0.5% Bi mole fraction in the InAsSbBi active region. A low growth temperature was utilized to facilitate the incorporation of Bi, resulting in a minority carrier lifetime on the order of 24 ns in the InAsSbBi active region. Nevertheless, the detectors exhibit a quantum efficiency of 17% at 3.3 μm wavelength with a dark current density of 50 μA/cm2 at 150 K and −0.4 V bias and the strong photoresponse turn-on characteristic of a random alloy at 4.32 μm wavelength and 150 K. A shot noise-equivalent irradiance analysis indicates that this detectors' dark-current-limited noise-equivalent irradiance of 1012 cm−2 s−1 is two orders of magnitude greater than the Rule 07 expectation for this cutoff, and dark-current-limited shot noise-equivalent irradiance performance transitions to photon-limited at 1.7 × 1015 photons/cm2 s. [ABSTRACT FROM AUTHOR]

The effect of majority carrier concentration and minority carrier lifetime on the performance of mid-wave infrared ( λ cutoff = 5.5 μ m) nBn detectors with variably doped InGaAs/InAsSb type-II superlattice absorbers is investigated. The detector layer structures are grown by molecular beam epitaxy such that their absorbing layers are either undoped, uniformly doped with a target density of 4 × 1015 cm−3, or doped with a graded profile, and variable-area mesa detector arrays are fabricated. Each material's temperature-dependent minority carrier lifetime is determined by time-resolved photoluminescence, and majority carrier concentration is extracted from capacitance–voltage measurements. Detector performance is evaluated with dark current and photocurrent measurements, from which quantum efficiency and shot-noise-limited noise-equivalent irradiance are calculated. The two doped detectors have lower dark current densities compared to their undoped counterpart due to the reduction in diffusion current as well as suppression of depletion current. Although both intentionally doped devices exhibit lower minority carrier lifetimes relative to the undoped device, the device with graded doping maintains a comparable quantum efficiency to the undoped device. Ultimately, the graded doping structure exhibits the highest sensitivity with a shot noise-limited noise-equivalent irradiance of 6.3 × 1010 photons/cm2 s in low-background light conditions, within a factor of 4× of an infrared detector pixel with Rule 07 dark current density and unity quantum efficiency. A detailed analysis of the dark current, quantum efficiency, and minority carrier lifetime provides insight into the material and device design factors that must be considered to realize a device with optimal sensitivity. [ABSTRACT FROM AUTHOR]

We analyze temperature-dependent photoluminescence (PL) behavior of patterned InAs/GaAs quantum dots (PQDs) formed by selective area epitaxy using metalorganic chemical vapor deposition. The processing scheme, described here, yields an ensemble of electronically isolated PQDs with PL characteristics that significantly differ from self-assembled (SA) QDs since neither a wetting layer nor neighboring QDs are available for coupling. The isolated nature of the PQDs supports a non-Fermi (nonequilibrium) carrier distribution which yields very different PL characteristics compared to the Fermi (equilibrium) distribution of the SAQDs especially at temperatures >100 K. Thus, the PQDs demonstrate a constant PL linewidth within the temperature range of 80–300 K along with improved temperature stability of PL intensity in comparison to SAQDs. The increased temperature stability allowed by electronic isolation may prove very important for high speed, temperature-insensitive QD laser development. [ABSTRACT FROM AUTHOR]

The authors investigate the etch modes of GaSb (100) through use of Arsenic (As2) based in situ etching. Three distinct etch modes result from temperature dependent in situ etching. The authors have used this in situ etch process on highly strained (In)GaSb quantum wells (QWs) and have studied the dependence of the in situ etching on substrate temperature and indium composition in the quantum well. The etched quantum wells are capped with an Al0.5Ga0.5Sb barrier and the photoluminescence properties are studied. The authors observe inhomogeneous broadening indicating the possible presence of quantum-sized features with different shapes and sizes. [ABSTRACT FROM AUTHOR]