Analytic modeling of sensitivity in diffusion-limited type-II superlattice mid-wave infrared nBn photodetectors for design optimization for low-irradiance conditions

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.