Diethyldisulphide as sulphur precursor for the low temperature metalorganic vapour-phase epitaxy of ZnS: growth, morphology and cathodoluminescence results

We report on the atmospheric pressure metalorganic vapour-phase epitaxy (MOVPE) growth of ZnS using diethyldisulphide (Et2S2) as sulphur precursor in combination with electronic grade dimethylzinc:triethylammine (Me2Zn:Et3N). Et2S2 is used here for the first time as a substitute of diethylsulphide (Et2S) to achieve low temperature ZnS growth in pyrolytic MOVPE. It is demonstrated that Et2S2 lowers the temperatures of the process by almost 150°C with respect to Et2S, leading to growth rates in excess of 0.5 um/h just above 400°C. Scanning electron microscopy observations and 10 K cathodoluminescence (CL) measurements performed on the as-grown samples are also reported. CL spectra show both free-to-bound and intense self-activated band emissions peaked at 3.683 and 2.58 eV, respectively. These emissions are attributed to unintentional Na and halogen (most probably Cl) doping of ZnS epilayers, likely arising from both Et2S2 and Me2Zn:Et3N precursors. Finally, monochromatic CL images of the samples demonstrate the interplay between point defects induced radiative emissions and non-radiative recombinations associated with the epilayer extended defects.