Electrical and optical performance of InAs/GaSb superlattice LWIR detectors

InAs/GaSb superlattices are a promising technology for long-wave and very-long-wave infrared photodetectors. Present detectors at these wavelengths are mostly built using bulk HgCdTe (MCT) alloys, where the bandgap is controlled by the mercury-cadmium ratio. In contrast, InAs/GaSb heterostructures control the bandgap by engineering the widths of the layers making up the superlattice. This approach is expected to have important advantages over MCT, notably the tighter control of bandgap uniformity across a sample and the suppression of Auger recombination. InAs/GaSb superlattices have a potential advantage in temperature of operation, uniformity and yield. To realize their inherent potential, however, superlattice materials with low defect density and improved device characteristics must be demonstrated. Here, we report on the growth and characterization of a 9.7 mu m cutoff wavelength InAs/GaSb superlattice detector, with a resistance-area product of R(0)A = 11 Omega cm(2) at 78 K, and an 8.5 mu m cutoff diode with a resistance-area product of R(0)A = 160 Omega cm(2) at 78 K. The devices are p-i-n diodes with a relatively thin intrinsic region of depth 0.5 mu m as the active absorbing region. The measured external quantum efficiencies of 7.1% and 5.4% at 7.9 mu m are not yet large enough to challenge the incumbent MCT technology, but suggest scaling the intrinsic region could be a way forward to potentially useful detectors.