PIXE and RBS Investigation of Growth Phases of Ultra Thin Chemical Bath Deposited CdS Films
School of Engineering
Polycrystalline CdS films, with thicknesses typically 20–180 nm, have been chemically deposited on glass substrates using an ammonia–cadmium–thiourea reaction solution. Film elemental composition, thickness and microstructure have been examined using proton-induced X-ray emission, Rutherford backscattering and atomic force microscopy. Analysis indicates that the stability of the deposition temperature plays a critical role in CdS film growth and composition. Films deposited with high temperature stability (60±0.5°C) show a consistent 1:1 Cd:S atomic ratio for all stages of film growth, and have good substrate adhesion. Films deposited with lower temperature stability (60±4°C) show initial high S concentrations, followed by a rapid increase in Cd concentration, until a final 1.2:1 Cd:S ratio is achieved. A mechanism is proposed to explain this difference in film composition and properties.