Effects of Substrate Temperature on the Properties of Hydrogenated Nanocrystalline Silicon Thin Film Grown by Layer-by-Layer Technique

Nanocrystalline silicon (nc-Si) thin films prepared by layer-by-layer (LBL) technique were studied. The LBL technique involves periodic interruption of the deposition process whereby the silane diluted in hydrogen plasma discharge is stopped for a fixed period of time during which the growth surface is treated with hydrogen plasma discharge. This technique controls the crystallite size in the film structure. The films are grown at different substrate temperatures ranging from room temperature to 400degC. The dependence of the optical and structural properties of the films on the substrate temperature is investigated using optical transmission, X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy technique. The effects of substrate temperature were studied and these properties showed strong dependence on the substrate temperature. Initial increase in the substrate temperature to 200degC resulted in a blue shift in the absorption edge but higher substrate temperature shifted it back towards lower energy. Higher substrate temperatures also lowered the hydrogen content in the film and increased the concentration of monohydride bonds in the film structure. Increase in crystallinity was observed with increase in substrate temperature.