Increased Lifetime and Decreased Dark Current in Ga-Containing Longwave Infrared (LWIR) Type-II Superlattices (T2SL) through Defect Identification and Mitigation

Absorber layers based on Type-II superlattices (T2SLs) composed of III-V compound semiconductors (e.g. GaSb and InAs) are a promising sensor technology for infrared imaging; however, dark currents and short carrier lifetimes in the Ga-containing T2SL are significant problems. It is presently suspected that the short carrier lifetimes and some dark current arise due to a native point defect, possibly the Ga antisite (a Ga atom on the Sb sublattice), creating a mid-gap state within the T2SL band gap that facilitates Shockley-Read-Hall generation/recombination. We propose to use first principles calculations to verify the suspect defect and evaluate its impact on lifetimes and dark currents, and study its impact as a function of position within the superlattice period. Other native defects will also be examined. Molecular dynamics molecular beam epitaxy growth simulations will then be used to evaluate growth strategies that minimize the concentration of the key defects. Experiments will then be performed to verify the theoretical understanding and optimize a growth process based on the theoretical predictions. Approved for Public Release 14-MDA-8047 (14 Nov 14)