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(SCNR 2 ) 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(CNR 2 ) 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 (Zn x Cd 1− x S) 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. Zn x Cd 1− x S 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.