Current-matching versus non-current-matching in long wavelength interband cascade infrared photodetectors

We report on a comparative study of two sets of different long-wavelength (LW) interband cascade infrared photodetectors (ICIPs) based on a type-II InAs/GaSb superlattice. The devices in one set have a current-matched configuration while those in the other set are non-current-matched. It is shown that carrier transport in these LW ICIPs at high temperatures is diffusion limited and the diffusion length is estimated to be longer than or comparable to 0.5 μm at various temperatures. By comparing the two sets of devices, we demonstrate the necessity of current-matching to maximize utilization of absorbed photons for an optimal responsivity and the correlation of reduced responsivity with light attenuation in the optically deeper stages for non-current-matched ICIPs. However, the device performances for both sets are comparable in terms of detectivity. Electrical gain exceeding unity is observed, which is more significant in the last stage of non-current-matched ICIPs than in any other stages in order to obtain photocurrent continuity. The significant electrical gain enabled an appreciable responsivity in non-current-matched ICIPs and resulted in Johnson-noise limited detectivities as high as 2.4 × 108 Jones at 300 K, which substantially exceeds the reported value (e.g., 4.0 × 107 Jones) for commercial uncooled mercury cadmium telluride detectors.