Growth and Electrical Properties of Zinc-Cadmium Sulfide Graded-Band-Gap Crystals

Large quasi-single crystals of ZnxCd1−xS with increasing x along the growth direction, have been successfully grown by vapor-growth techniques. Typical dimensions are 15×3×4 mm. The growth mechanism is studied and, as a result, it is believed that the thermal conductivity plays a decisive role. Position-dependent optical and electrical studies on these crystals have revealed that the crystals with a slowly varying composition can be described by a graded band gap while the properties of crystals having a more abrupt change in composition are determined by lattice defects. Most of the crystals exhibit photoluminescence and high-field electroluminescence at low temperatures. From the optical and electrical data an energy-band diagram for graded ZnxCd1−xS is deduced with the position-dependent band gap accounted for by the position-dependent electron affinity.