Nanostructures for Dislocation Blocking in Infrare

Current state of the art LWIR and VLWIR focal plane arrays are typically fabricated with HgCdTe epilayers grown on expensive and limited-size CdZnTe substrates. The transition to silicon-based substrates, which are much cheaper and available in large sizes, has been hindered by high dislocation densities in HgCdTe epilayers resulting from lattice mismatch-induced strain. We propose the novel approach of nanopatterning silicon-based substrates to exploit strain relaxation in 3-dimensions before growing high quality CdTe buffer layers and subsequent LWIR HgCdTe epilayers. The selective area epitaxy of CdTe at the nanoscale followed by lateral epitaxial overgrowth and then coalescence, as demonstrated in Phase I, will result in high quality CdTe layers. Strategies to improve the coalescence of CdTe on the nanopatterned substrates and resolve thermal mismatch strain by novel nanoscale geometries will be developed and implemented in the proposed Phase II program. LWIR HgCdTe will be grown on silicon-based nanopatterned substrates by molecular beam epitaxy and extensive material and interface characterizations will be performed to analyze the advantages of nanoscale patterning. Single element detectors and test arrays will be fabricated from the HgCdTe epilayers and characterized extensively for electrical and optical performance.