Structure defects and phase transition in tellurium-doped ZnSe crystals

ZnSe crystals grown from the melt by Bridgman method are characterized by the presence of such microstructure defects as pores and solid-phase inclusions, grain boundaries and packing defects of twinning type. Microstructural and X-ray analysis of the grown crystals has shown that optical non-uniformity is mainly due to coherent twinned interlayers related to the phase transition wurtzite (W) --> sphalerite (S) on cooling which is incomplete over (0001)W parallel to(111)S planes. The tellurium dopant affects favorably the optical uniformity and degree of structural perfection of ZnSe(Te) crystals. This is due primarily to the sphalerite structure being completely stabilized during the growth process and the absence of twinning type packing defects (PD). Concentration of tellurium is determined which is sufficient to make complete the W --> S phase transition. (C) 1999 Elsevier Science B.V. All rights reserved.