Introduction

Abstract

Interest in optical devices which can operate in the visible spectrum has motivated research interest in the semiconductors of wide bandgap II–VI compounds, such as ZnSe, ZnS, ZnTe, CdS and CdSe and their solid solutions, which are expected to be the vital materials for high-performance optoelectronics devices such as light-emitting diodes (LEDs) and laser diodes operating in the blue spectrum and ultraviolet detectors. Compounds of the group II–VI elements, specifically, ZnS, ZnSe, ZnTe, CdS and CdSe, providing as matrix materials for doping with transition metal as activator ions, also promise wide coverage of the mid-IR spectrum for the development of solid-state lasers. In the bulk growth of some technologically important semiconductors, growth technique of physical vapor transport (PVT) have significant advantages over melt growth because of the high melting points of these materials. The continued improvement in overall device performance requires bulk crystals with less structural defects such as twins, lattice strain, dislocations, grain boundaries and second phase inclusions. The electrical and consequently the optical properties of the materials depend on the deviation from stoichiometry, the impurity or dopant distribution, and native point defects. The compositional homogeneity becomes extremely important for the ternary alloys because the non-uniformity in composition implies a response at different wavelengths across the crystal wafer. The realization of high performance devices is dependent on the routine production of high-quality, single-crystalline wafers which requires systematic investigations on the correlations between the process conditions of the PVT and various properties of grown crystal.