Non-cryogenic operation of HgCdTe infrared detectors

Abstract

High sensitivity HgCdTe infrared detector arrays operating at 77 K can be tailored for response across the infrared spectrum (1 to 14 μm and beyond), and are commonly utilized for high performance infrared imaging applications. However, the cooling system required to achieve the desired sensitivity makes them costly, heavy and limits their applicability. Reducing cooling requirements and eventually operating at temperatures that could be reached with thermoelectric coolers can lead to lighter and more compact systems. However, at these elevated temperatures, the absorber layer becomes intrinsic, carrier concentrations are high and Auger processes typically dominate the dark current and noise characteristics. Auger processes can be suppressed by placing the absorber layer between an exclusion junction and an extraction junction at reverse bias. This reduces the minority carrier concentration in the absorber by several orders of magnitude below thermal equilibrium. The majority carrier concentration also drops significantly below thermal equilibrium to maintain charge neutrality, eventually reaching the extrinsic doping level. This device architecture produces a lower dark current density and lower noise at non-cryogenic temperatures than standard p-n junction photodiodes. Due to the precise control of the layer's thicknesses and compositions that could be achieved with molecular beam epitaxy (MBE), this technique is the method of choice for implementing these novel non-equilibrium devices. In this work, we analyze Auger suppression in HgCdTe alloy-based device structures and determine the operation temperature improvements expected when Auger suppression occurs. We identified critical material (absorber dopant concentration and minority carrier lifetime) requirements that must be satisfied for optimal performance characteristics. Experimental dark current-voltage characteristics between 120 and 300 K are fitted using numerical simulations. Based on this, the negative differential resistance (NDR) observed in experimental data is attributed to the full suppression of Auger-1 processes and the partial suppression of Auger-7 processes. We will also present an analysis and comparison of our theoretical and experimental device results in structures where Auger suppression was realized.