Investigation of Modified Bridgman Grown CdTe_x Crystals and Their Characterization

摘要

Growth procedure was modified with off-stoichiometric charge using excess tellurium solution (different Te composition 0.9, 1.1, 1.2, and 1.3 weight percentages in the initial charge). Graphitic carbon coating of the inner wall of the ampoule was carried out. The rotation of the ampoule with the molten charge was carried out before lowering the same for crystal growth. The grown crystals were characterized by X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDAX), photoluminescence, and chemical etching studies. Increasing tellurium content in the charge in excess of 1.2 weight percent lead to cracks and twinning. The off-stoichiometric melt grown crystals crystallize in zinc blende structure with lattice parameter 6.482A. Excess tellurium content in the crystal decreases the intensity of the prominent peak along the (111) direction in the XRD spectrum. The defect levels introduced by Te precipitates for various tellurium rich compositions in CdTe_x crystals are identified from the photoluminescence spectra. The off-stoichiometric charge composition influences enormously the defect density and the crystalline quality of the grown crystals. The results on the optimization of the growth procedure and influence of off-stoichiometric compositions are discussed.