Metalorganic vapour phase epitaxy growth of ZnS layers by (t-Bu)SH and Me2Zn:Et3N precursors

We report for the first time on the metalorganic vapour phase epitaxy of ZnS layers on (100)GaAs substrates by using tertiary-butyl-mercaptan ((t-Bu)SH) and dimethylzinc:triethylamine adduct (Me(2)Zn:Et(3)N) as sulphur and zinc precursors, respectively. We demonstrate that the combination of Me(2)Zn:Et(3)N with (t-Bu)SH avoids the occurrence of pre-reactions even under atmospheric pressure conditions, allowing the growth of good quality single crystalline ZnS epitaxial layers. However, low pressures (ca. 300 mbar) were necessary to limit the gas phase depletion of the precursors in the reactor chamber, a consequence of the low thermal stability of (t-Bu)SH and Me(2)Zn:Et(3)N. ZnS growth rates as high as 2.4 µm/h were thus obtained at around 346°C, the growth process being kinetically limited at lower temperatures. The surface of the epilayers was invariably smooth and mirror-like, its average surface roughness being typically around a few nanometers. Finally, no apparent diffusion of Zn and S into the GaAs substrate was observed for samples grown at 350°C, whereas Ga and As were detected into regions of the ZnS epilayers close to the ZnS/GaAs heterointerface.