Thio- and Dithio-Biuret Precursors for Zinc Sulfide, Cadmium Sulfide, and Zinc Cadmium Sulfide Thin Films

Zinc and cadmium complexes of 1,1,5,5-tetraalkyl-2-4-dithiobiurets [M(N(SCNR2)2)2] [M = Zn, R = methy (1), ethyl (2) and M = Cd, R = methyl (4), ethyl (5)] and 1,1,5,5-tetraalkyl-2-thiobiurets [M(SON(CNR2)2)2] [M = Zn, R = isopropyl (3) and M = Cd, R = isopropyl (6)] have been synthesized. The single crystal X-ray structures of complexes (2), (3), (4), and (5) were determined. Thermogravimetric analysis confirmed that all six complexes decomposed in a single step to their corresponding metal sulfides. The complexes were used as single source precursors for the deposition of zinc sulfide (ZnS), cadmium sulfide (CdS), and zinc cadmium sulfide (ZnxCd1−xS) thin films by aerosol assisted chemical vapor deposition (AACVD). The zinc complexes (1) and (3) deposited cubic ZnS films with small rods and granular crystallites at 300 and 350 °C, whereas at 400 and 450 °C hexagonal ZnS with granular crystallites were dominant. Complex (2) gave granular hexagonal ZnS films at all deposition temperatures. Cadmium complexes (4), (5), and (6) gave granular hexagonal CdS films at all deposition temperatures. ZnxCd1−xS films were deposited by varying the relative concentration of precursors (1) and (4), (2) and (5), and (3) and (6) at 400 °C. The formation of a solid solution was confirmed by UV−vis spectroscopy and powder X-ray diffraction. The morphology of the films was studied by scanning electron microscopy and atomic force microscopy. The elemental composition of films was confirmed by energy dispersive X-ray spectroscopy.