ALD PASSIVATION OF SLS DETECTORS

Pixel sidewalls of antimony-based type-II strained layer superlattices (SLS) with infrared energy bandgaps have electron accumulation (in n-type SLS) or electron inversion (in p-type SLS) surface layers that contribute leakage current that affects detector performance. These conductive surfaces are a consequence of surface Fermi level pinning in these materials and have to be prevented to address the leakage problem. Atomic Layer Deposition (ALD) is a promising approach to such passivation, especially given its ability to conformally coat the deep trenches that need to be etched between short-pitch pixels and dualband pixels. In Phase I, we developed an ALD recipe to passivate deep-dry-etched pixels of n-type SLS lattice-matched to GaSb, achieving performance identical to shallow-etched pixels from the same material. Phase II will focus on two parallel paths for boosting quantum efficiency (QE): p-type GaSb-SLS and n-type AlSb-SLS (SLS lattice-matched to AlSb). Higher QE results from greater electron diffusion length in the former, and from a reduction in superlattice period in the latter. Our goal is to achieve > 80-60% QE in SLS FPAs with cutoffs from 10-13 microns. Passivating p-type SLS is a hard problem. In the Phase I Option, we propose to experimentally investigate Zn-based ALD to modify surface Fermi levels, an approach patented by the Airforce.