Epitaxial growth of films of ZnS evaporated on to NaCl

Abstract

Films of ZnS were deposited on to NaCl by vacuum evaporation. The influence of the growth conditions on the structure of the films was studied by transmission electron microscopy. The most important single factor in producing the widest range of epitaxial substrate temperatures and the most perfect films was the use of focused electron-beam evaporation. Contamination raised the minimum substrate temperature for epitaxial growth. It also resulted in the incorporation of doubly positioned wurtzite-structure grains in the sphalerite-structure films. Co-evaporation of an excess of either Zn or S with ZnS produced sphalerite-structure films containing singly positioned wurtzite grains. The use of conventional hot tantalum evaporators resulted in the incorporation of 0·2 wt.% of tantalum in the films and in poor structural quality. Reproducible current-voltage characteristics were obtained in the best structural quality films. These current-voltage characteristics could be understood in terms of the effect of Schottky barriers but not of space-charge-limited currents.