High Purity 6-inch+ Diameter Single Crystal Germanium Wafers for Dark Matter CCD Photon Detectors

The Department of Energy (DOE) Office of High Energy Physics Research supports user facilities studying dark energy. The facilities include ground-based telescopes that would benefit from the availability of semiconductor focal planes with sensitivity ranging into the infrared. Greater infrared sensitivity will provide observation of red-shift data on the largest possible number of astronomical objects. The manufacture of germanium CCDs now appears possible. The addition of high-purity germanium as the substrate for the CCDs will greatly improve the sensitivity and manufacture of these CCDs. High-purity 150-mm diameter semiconductor-quality high-purity germanium wafers are being developed to fill this need. During Phase I, high-purity germanium crystals were grown, sliced, lapped, polished, and shaped into standard form-factor 150-mm diameter semiconductor wafers 675 microns thick. Preliminary testing of these wafers indicates compatibility with the processing required to make them into CCDs. Phase II will see more high-purity wafers produced and tested under varied crystal-growth conditions to develop high-purity germanium substrates that can be fabricated into working CCDs. The goal is to demonstrate working high-purity germanium CCDs by the end of Phase II.Commercial Applications and Other BenefitsThe crystal-growth variations to be researched during Phase II will have direct positive impact on the DOE high-energy physics programs with collateral benefits to satellite-based research and tactical imagers. In addition, the crystal research will positively impact the manufacture of germanium gamma-ray detectors for nuclear security, nuclear research and nuclear-medicine applications.