Chalcogen Precursor Effect on Cold-Wall Gas-Source Chemical Vapor Deposition Growth of WS2

Tungsten disulfide (WS2) films were grown on c-plane sapphire in a cold-wall gas-source chemical vapor deposition system to ascertain the effect of the chalcogen precursor on the film growth and properties. Tungsten hexacarbonyl (W(CO)(6)) was used as the tungsten source, and hydrogen sulfide (H2S) and diethyl sulfide (DES-(C2H5)(2)S) were the chalcogen sources. The film deposition was studied at different temperatures and chalcogen-to-metal ratios to understand the effect of each chalcogen precursor on the film growth rate, thickness, coverage, photoluminescence, and stoichiometry. Larger lateral growth was observed in films grown with H2S than DES. The reduced lateral growth with DES can be attributed to carbon contamination, which also quenches the photoluminescence. Thermodynamic calculations agreed well with the experimental observations, suggesting formation of WS2 with both sulfur precursors and additional formation of carbon when deposition is done using DES.