HgCdTe Auger-Suppressed Infrared Detectors Under Non-Equilibrium Operation.

Abstract

A nearly universal goal for infrared photon detection systems is to increase their operating temperature without sacrificing performance. The limiting factor for cooling requirements is the dark current in the detector devices. The dark current in HgCdTe infrared detectors is limited by Auger processes at near-room temperatures of operation. Device designs based on non-equilibrium operation in HgCdTe devices have been proposed to overcome this. In this work, we study non-equilibrium operation in reverse-biased HgCdTe detectors in order to achieve Auger suppression and decrease the dark current. Finite-difference methods are used to accurately model the devices, including self-consistent, steady-state solutions of Poisson’s equation and the carrier continuity equations for carrier densities. It is found that background-limited performance can be achieved in ideal Auger-suppressed HgCdTe devices operated at 180 K for mid-wave infrared detection, opening the possibility to use thermoelectric cooling, and operated at 120 K for long-wave infrared detection. The material structure and doping levels in an HgCdTe detector with cutoff wavelength λc=5.5 µm at 200 K are optimized to maximize Auger suppression. The most critical parameters are found to be those of the absorber layer, especially the doping level and concentration of traps. We also present full temperature-dependent device characterization of fabricated HgCdTe photodiodes, designed using our device model, with cutoff wavelength of λc=10 μm at 100 K. HgCdTe wafers are grown by molecular beam epitaxy by EPIR Technologies, Inc. Devices are fabricated by the US Army Research Laboratory and the University of Michigan. Clear evidence of Auger suppression is observed in the experimental current-voltage data between 120 K and room temperature with up to 50 % decrease of the dark current as the reverse bias is increased. The measured detectivity D* with black-body of 500 K, field-of-view of 90 degrees, and chopper frequency of 1 kHz is in the low-10^9 cm.Hz^0.5/W at 120 K and the mid-10^7 cm.Hz^0.5/W at 300 K. The electrical characteristics of the devices are fitted using our device model. Leakage current induced by traps and impurities in the material causing Shockley-Read-Hall recombination limits the saturation current after Auger suppression.