Low Pressure MOVPE Growth of ZnS Epilayers by Using Dimethyldisulphide Precursor

Abstract

We report on the low pressure metalorganic vapour-phase epitaxy of ZnS using dimethyldisulphide (Me 2 S 2 ) as novel sulphur precursor in combination with dimethylzinc:triethylammine. The pyrolytic growth of ZnS by Me 2 S 2 is investigated and compared with the use of diethyldisulphide (Et 2 S 2 ). The growth rate of ZnS is studied as a function of growth and precursor source temperatures. Me 2 S 2 requires growth temperatures only about 60 °C higher with respect to that needed by Et 2 S 2 ; S-rich conditions were obtained for Me 2 S 2 source temperatures down to 5 °C. Mass spectrometry fragmentation experiments performed on the Me 2 S 2 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 Me 2 S 2 decomposition could occur mainly via the sequential loss of methyl radicals. Also, the occurrence of the strong S-S bond in the Me 2 S 2 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 Me 2 S 2 is studied by high resolution X-ray diffraction measurements performed on ZnS/GaAs samples grown at 460 °C.