Low pressure MOVPE growth of ZnS epilayers by using dimethyldisulphide precursor

We report on the low pressure metalorganic vapour-phase epitaxy of ZnS using dimethyldisulphide (Me2S2) as novel sulphur precursor in combination with dimethylzinc:triethylamine. The pyrolytic growth of ZnS by Me2S2 is investigated and compared with the use of diethyldisulphide (Et2S2). The growth rate of ZnS is studied as a function of growth and precursor source temperatures. Me2S2 requires growth temperatures only about 60°C higher with respect to that needed by Et2S2; S-rich conditions were obtained for Me2S2 source temperatures down to 5°C. Mass spectrometry fragmentation experiments performed on the Me2S2 ion allow to determine the molecule relative bond strenghts, as well as to propose possible pyrolytic decomposition paths for the new precursor. It is suggested that Me2S2 decomposition could occur mainly via the sequential loss of methyl radicals. Also, the occurrence of the strong S-S bond in the Me2S2, molecule destabilises the S-C bond leading to relatively lower growth temperatures than expected for dimethylsulphide. Finally, the overall crystalline quality of ZnS epilayers grown by Me2S2 is studied by high resolution X-ray diffraction measurements performed on ZnS/GaAs samples grown at 460°C.