The semiconductor minority carrier lifetime contains information about several important material properties, including Shockley–Read–Hall defect levels/concentrations and radiative/Auger recombination rates, and the complex relationships between these parameters produce a non-trivial temperature-dependence of the measured lifetime. It is tempting to fit temperature-dependent lifetime data to extract the properties of the Shockley–Read–Hall recombination centers; however, without a priori knowledge of the distribution of the Shockley–Read–Hall states across the bandgap, this fit problem is under-constrained in most circumstances. Shockley–Read–Hall lifetime data are not well-suited for the extraction of Shockley–Read–Hall defect levels but can be used effectively to extract minority carrier recombination lifetimes. The minority carrier recombination lifetime is observed at temperatures below 100 K in a Si-doped n-type InGaAs/InAsSb superlattice, and deviation from its expected temperature-dependence indicates that the capture cross section of the defect associated with Si-doping has an activation energy of 1.5 meV or a characteristic temperature of 17 K. This lower temperature regime is also preferrable for the analysis of the physics of defect introduction with displacement-damage-generating particle irradiation.
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.
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