Effects of Deposition Parameters and Conditions on the Physical and Electro-Optical Properties of Buffer Solution Grown CdS Thin Films

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CdS films were grown by a buffer solution growth technique using CdSO 4 as the cadmium source, thiourea as the sulphur source, and (NH 4 ) 2 SO 4 as the buffer. It has been shown that by varying the ratio (R c ) of molar concentration of (NH 4 ) 2 SO 4 to that of CdSO 4 in the solution, with other deposition parameters fixed, the growth rate of CdS films, and hence, its thickness can be adjusted. For [CdSO 4 ] 0.002 M, a CdS film of maximum thickness of 120 nm was obtained for R c = 10, above which the film gradually became thinner because of the slow release of Cd 2+ into the solution to participate in the heterogeneous CdS film deposition, and below which thin films (50 to 80 nm) were grown because of the undesirable homogeneous precipitation of CdS particles in the solution. When the deposition solution was not covered during CdS film deposition, a loss of deposition solution via evaporation was observed causing a degradation of the film properties in the form of reduced CdS film thickness, relatively non-uniform film surface, high dark resistivity and optical energy gap.