Growth of SrS single crystals by physical vapor transport

Abstract

Alkaline earth sulfides have recently been found to have interesting luminescent properties for applications in thin film electroluminescence devices. Strontium sulfide doped with rare earth ions is one of the most promising of these materials for blue or white emitting displays. However, hardly anything is known about the basic material properties of the IIa–VI semiconductors, one of the reasons being the difficulty in growing single crystals of these materials. Thus, we have investigated the crystal growth and properties of SrS. In preliminary experiments using the laser heated pedestal growth (LHPG) technique, the high evaporation rate of the SrS prevented the formation of a stable molten zone. However, the recondensed material in the system was found to be pure, stoichiometric SrS and, therefore, vapor phase transport appeared a more promising approach. Using the physical vapor transport (PVT) technique, we have been able to grow SrS crystals about 1 cm in diameter and 1 cm in length containing only a few grains. Crystals have been grown in a high temperature graphite furnace in a graphite ampoule at 1650°C and 10 -4 Torr. The as-grown crystals were slightly colored. Annealing in an argon atmosphere at 2000°C resulted in colorless crystals. The coloration of the as-grown crystals may result from carbon incorporation during growth.