Bulk InAs(x)Sb(1-x) is an infrared detector material that promises higher quantum efficiency than antimony-based superlattices in the longwave infrared (LWIR). This is due to the longer diffusion length of minority carrier holes in the bulk than in superlattices where they are localized. No native substrate exists for lattice-matched growth of InAs(x)Sb(1-x) material with LWIR bandgaps. So a key challenge is finding a suitable buffer that will minimize the crystal dislocation defects that will inevitably result from lattice-mismatched growth of InAs(x)Sb(1-x) on a substrate such as GaSb or GaAs. Such defects provide leakage paths and increase dark current. They also reduce minority carrier lifetime which reduces diffusion length and therefore quantum efficiency. Eliminating these defects is key to device performance. One solution is a suitable metamorphic buffer layer that filters out crystal dislocations and provides a template for the defect-free growth of the subsequent device layers. In Phase I, a QmagiQ-led team of device, material growth and material analysis experts developed such buffers and demonstrated high-performance focal plane arrays with cutoff wavelengths of 5 and 7 microns. In Phase II, we will build on this work and extend cutoff wavelength to the desirable 10-12 microns region.
