Synchrotron topography characterization of ZnTe single crystals

(111) Wafers sliced from a single-crystal boule of ZnTe grown by horizontal physical vapor transport have been characterized using synchrotron white-beam X-ray topography. The presence of dislocation slip bands, subgrain structures, and long, thin 180° rotational twin lamellae was revealed. Distorted regions exhibiting radial lattice rotation were also observed near the crystal edges. One of these regions is clearly the source for the generation of some of the slip bands observed in the crystals. The slip bands were observed to break up the ordered dislocation cell structures comprising the subgrain boundaries, indicating that the dislocation cell structure appears earlier during the growth process, and that the slip dislocations appear later, perhaps during the postgrowth cooling process. This may also be an indication that modification of the cooling rate could have a significant effect on the final defect microstructure, with for example more rapid cooling giving rise to more slip which could obscure the true growth-defect microstructure. The initiation of slip at regions of stress concentration, such as at lateral twin boundaries, and at the junctions of subgrain boundaries and twin boundaries, was also revealed. The asymmetrical distribution of slip bands either side of the twinned region of crystal suggests that twin boundaries can act as barriers for slip. Several types of detailed twin boundary configuration were determined from the topographs. Using a combination of white-beam X-ray topography and Nomarski interference microscopy, the three-dimensional shapes of the twin boundaries were determined. Approximate atomic structures at these boundaries are presented. Possible mechanisms for the production of a long thin twin lamella, oriented at a small angle to the growth axis, are discussed.