Numerical Simulation and Analytical Modeling of InAs nBn Infrared Detectors with p-Type Barriers

Abstract

This paper presents one-dimensional numerical simulations and analytical modeling of InAs nBn detectors having n-type barrier layers (BLs) with donor concentrations ranging from 1.8 × 1015 cm−3 to 2.5 × 1016 cm−3. We consider only “ideal” defect-free nBn detectors, in which dark current is due only to the fundamental mechanisms of Auger-1 and radiative recombination. We employ a simplified nBn geometry, with the absorber layer (AL) and contact layer (CL) having the same donor concentration and comparable thicknesses, to reveal more clearly the underlying device physics and operation of this novel infrared detector. We examine quantitatively the three space-charge regions in the nBn detector with an n-type BL, and determine a criterion for combinations of bias voltage and BL donor concentration that allow operation of the nBn with no depletion region in the narrow-gap AL or CL. We determine the quantitative characteristics of the valence band (VB) barrier that is present for an n-type BL but not for a p-type BL. Solving Poisson’s equation in the uniformly doped BL yields analytical expressions for the VB barrier height versus bias voltage, and an approximate expression for the crossover voltage for the onset of a depletion region in the AL. Our simulations lead to a new model for the ideal nBn with an n-type BL that consists of two ideal back-to-back photodiodes connected by a voltage-dependent series resistance representing the BL. Increasing the BL donor concentration lowers exponentially the mobile hole concentration in the BL, thereby exponentially increasing the BL series resistance. Reductions in dark current and photocurrent due to the valence barrier in the n-type BL only become appreciable when the BL series resistance becomes comparable to or exceeds the diffusion current resistances of the AL and CL.