X-ray diffraction analysis of melt-grown ZnGeP2 (ZGP)

Good quality large ZnGeP2 (ZGP) crystals have been grown by the horizontal gradient freezing (HGF) technique. Clusters of the disordered cubic ZGP str ucture assigned as beta-ZGP were identified within the ordered tetragonal m atrix (alpha-ZGP). Applying XRD analysis on poly- and single-crystalline sa mples followed by a whole pattern optimization (Rietveld technique) and a l ine profile fitting (LPF) analysis enabled the identification of the beta-p hase. It has been shown that the beta-ZGP clusters are coherently oriented with respect to the tetragonal matrix. New result on the thermal expansion of ZGP was obtained, supporting the appearance of order --> disorder transi tion in ZGP. A reduction in the residual absorption at the near IR could be observed as a result of post growth thermal annealing of ZGP in vacuum, fo llowed by a reduction in the relative amount of the disordered cubic compon ent. The above results suggest that point defects, which are considered to be responsible for the large absorption coefficient in the near IR, also re late to the presence of coherent beta-ZGP clusters. (C) 1999 Elsevier Scien ce B.V. All rights reserved.