The influence of source non-stoichiometry on the growth of crystalline films of zinc sulphide on silicon in ultrahigh vacuum

Abstract Single-crystal films of zinc sulphide were grown on silicon substrates by sublimation from a powder source in ultrahigh vacuum. The precise growth technique is very dependent on the zinc: sulphur ratio of the source material. Wide deviations from stoichiometry, ranging from 17% zinc rich to 7% sulphur rich, were found in the starting materials. In some cases, the zinc: sulphur ratio of the source was found to have changed during the growth cycle by as much as 19%. The results indicate that, although a near-stoichiometric source is preferred for ease of nucleation and for more perfect orientation and structure, particularly on (100) substrates, films grown from sources with a higher zinc content have a lower optical absorption and a smoother surface texture.