AFRL-OSR-VA-TR-2014-0375 Novel Substrates for Photodetectors

This research has investigated epitaxial InSb, CdTe, MgCdTe, and CdTe/MgCdTe double heterostructures grown on InSb (100) substrates using molecular beam epitaxy. State-ofthe-art materials quality has been successfully achieved in all of these materials, which have demonstrated record narrow X-ray diffraction line-widths, ultra-low defect density, and record long minority carrier lifetime of over 340 ns. All of these findings provide strong evidence that CdTe grown on InSb is highly suitable for use as a virtual substrate for multiple applications, including infrared detectors and the investigation of CdTe solar cells. 1. Objectives The next generation of IR sensors is likely to be based on large-format (megapixel) arrays of photodetectors with multi-spectral band capabilities. HgCdTe alloys and type-II superlattices based on GaSb substrates have been shown to be ideal for future mid-wave infrared (MWIR) and long-wave infrared (LWIR) photodetector applications. These materials have to be grown on suitable substrates that have large areas enabling low manufacturing cost of the arrays, as well as having similar bonding properties, lattice constants, and thermal expansion coefficients. This research program was initially funded for three years but support was later reduced to a level sufficient only for a single year of research due to sequestration of federal funds. Thus, the scope of the proposed research had to be substantially curtailed, and effort was concentrated mainly on the growth and optical characterization of CdTe/InSb and exactly-lattice-matched CdZnTe/InSb heterostructures.