MWIR InAsSb XBn detectors for high operating temperatures

An XBn photovoltaic device has a band profile similar to that of a standard homojunction p-n diode, except that the depletion region is made from a wide bandgap barrier material with a negligible valence band offset but a large conduction band offset. In this notation, "X" stands for the n- or p-type contact layer, "B", for the n-type, wide bandgap, barrier layer, and "n", for the n-type, narrow bandgap, active layer. In this work, we report on the fabrication of XBn devices, which were grown by Molecular Beam Epitaxy (MBE) on GaSb substrates. Each structure has an InAsSb active layer of thickness ∼1.5μm and a 0.2-0.5μm thick AlSbAs barrier layer. Good growth uniformity was achieved with lattice matching of better than 500ppm. Selected layers have been processed into devices which operate with a high internal quantum efficiency at a bias of ∼0.1-0.2V, and which exhibit a very low dark current due to the strong suppression of the current component due to bulk Generation-Recombination processes. From dark current measurements, a minority carrier lifetime of >670nS has been estimated in devices with an active layer doping of ∼4×10¹⁵cm^-3. In optimized, lattice matched, devices with this doping and an active layer thickness of 4μm, a cut-off wavelength of ∼ 4.0 - 4.1μm is expected at 160K, with a dark current density of ∼10^-6 A cm^-2 and a quantum efficiency of >70% (λ<4μm). These figures correspond to BLIP operation at 160K with a photocurrent to dark current ratio of ∼4 at f/3.