New model for the ideal nBn infrared detector

Abstract

This paper presents one-dimensional numerical simulations and analytical modeling of InAs nBn detectors having n-type barrier layers with donor concentrations ranging from 1.8×10¹⁵ 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. Our simulations lead to a new model for the ideal nBn with an n-type barrier layer (BL) that consists of two ideal backto- back photodiodes connected by a voltage-dependent series resistance representing hole conduction within the BL. Increasing the BL donor concentration lowers exponentially the hole concentration in the BL, thereby exponentially increasing the BL series resistance. Reductions in dark current and photocurrent due to the valence band barrier in the n-type BL only become appreciable when the BL series resistance becomes comparable to or exceeds the sum of the diffusion current resistances of the AL and CL. This new model elucidates the overwhelming importance of the electrical type and doping concentration of the BL to the operation of the nBn detector.