Type-II superlattice materials research at the Air Force Research Laboratory

Abstract

Type-II superlattice (SL) materials research in the Materials & Manufacturing Directorate of the Air Force Research Laboratory began in 1988. This materials system holds great promise as the III-V equivalent to HgCdTe alloys for infrared detection. Great progress has been made on the epitaxial growth of InAs/Ga_1-xIn_xSb superlattices in the past twenty years by a number of research groups. However, not all of the materials issues have been solved. To continue to resolve these limiting materials issues, basic superlattice materials, without photodiode fabrication, are used to characterize the impact of growth processes and SL design on the structural, electrical and optical properties. An integrated approach of theoretical modeling, in-house molecular beam epitaxy, and a host of materials measurement techniques is employed to study the optimization of the superlattices for infrared detection. In the past few years the majority of the samples grown in-house have been designed for the middle wavelength infrared (MWIR) band. However, there are challenges in applying MWIR SL growth optimization to longer wavelength SLs. Recent progress on understanding the complex interplay between InAs/GaSb superlattice composition and fundamental electrical and optical properties will be covered.