The Use of Hydrogen for Defect Reduction in Large Format Infrared Detector Materials

In Phase I we demonstrated a novel in-situ cleaning technique based on UV-activated surface reactions involving ozone and hydrogen to remove organic adsorbates and chemically-bonded impurities, e.g oxides, from the substrate surface. In Phase II the program will develop this process to significantly decrease the density of material defects in large-format, infrared, focal-plane arrays. Electrically-active defects impact array performance by increasing noise levels up to catastrophic degradation. The focus of this project is the elimination of active defects formed during molecular-beam epitaxy (MBE) of HgCdTe (the active layer in the arrays) on alternative substrates, i.e. materials other than lattice-matched CdZnTe. A significant fraction of as-grown defects nucleate at surface sites related to impurities or artifacts associated with ineffectual substrate cleaning prior to MBE growth. This will be demonstrated on alternative substrates, including InSb, GaAs, Ge and Si wafers using advanced surface characterization techniques, as well as through evaluation of HgCdTe epilayers grown on buffered InSb and GaAs. In addition, HgCdTe-based devices fabricated using photolytically cleaned substrates will be compared to ones fabricated using standard cleaning techniques to demonstrate this process. This will achieve the overall objective of significantly improving operability by reducing defects and dislocations in large-format infrared detector materials.