Growth and Characterization of High Quality, Low Defect, Subgrain Free Cadmium Telluride by a Modified Horizontal Bridgman Technique

Abstract

ABSTRACTA low stress modified horizontal Bridgman technique has been developed and used to grow low defect, large area, subgrain free CdTe crystals for use as substrates in the epitaxial growth of HgCdTe and related IR detector materials. CdTe wafers cut from horizontal Bridgman grown boules exhibit, resistivities in the 107ohm-cm range. Etch pit counts are in the 104cm−2 range. Etch pit patterns as well as x-ray topographs indicate the absence of low-angle grain boundaries. Double crystal x-ray rocking curves are single peaked and very narrow with FWHM(333) as low as 9 arc-sec. Rocking curves of FWHM(333) = 9 to 15 arc-sec, measured at several different laboratories, have been obtained for CdTe wafers cut from several boules. This is in contrast to standard vertical Bridgman grown CdTe samples, which generally show broader x-ray rocking curves sometimes with multiple peaks as a result of subrgrain structure. Low temperature (1.6–4.5 K) photoluminescence (PL) measurements on these low defect samples reveal bright edge emission lines which are the main feature of the spectrum. Additional bound exciton lines and other sharp features associated with donor and acceptor impurities are also present. The very weak defect band luminescence (1.40–1.46 eV) provides additional evidence of sample quality.