CVD of nanosized ZnS and CdS thin films from single-source precursors

A chemical vapor deposition (CVD) route to nanosized ZnS and CdS thin films was developed. The layers were deposited on SiO2 substrates in a N2 atmosphere at temperatures between 473 and 723 K using M(O-iPrXan)2 [M = Zn,Cd; O-iPrXan = S2COCH(CH3)2] as single-source precursors. Thermal decomposition and fragmentation of M(O-iPrXan)2 compounds were investigated by thermal analyses and mass spectrometry. The sulfide films were thoroughly characterized in their composition, nanostructure, and morphology by means of several analytical techniques. Surface and in-depth chemical composition was studied by X-ray photoelectron spectroscopy, X-ray excited Auger electron spectroscopy, and secondary ion mass spectrometry. Film nanostructure and surface topography were investigated as a function of the synthesis conditions by glancing incidence X-ray diffraction and atomic force microscopy, respectively. Optical absorption properties were also studied. Nanophasic and contaminant-free ZnS and CdS thin films with an average crystallite size lower than 25 nm were obtained. The layers mainly contained the hexagonal (alpha) sulfide phase and displayed a smooth and regular surface morphology. In the present work, the influence of synthesis conditions on film characteristics is analyzed and discussed. [Application: direct band-gap semiconductors].