Optical characterization of intrinsic poly silicon film for photovoltaic application on sapphire and TiO2 substrate by HWCVD

We have investigated the possibility of growing silicon films, 2 to 3 micron thick, from silane-hydrogen mixture, by hot wire chemical vapour deposition (HWCVD). Several substrates i) oriented TiO₂ layer on glass, ii) crystalline sapphire have been used in this work. The growth is performed in two stages; a) nucleation step using dilute mixture SiH₄:H₂ in the ratio 1:20 at 400 degC, followed by b) thickening step at 540 degC, in which SiH₄:H₂ ratio is gradually enhanced to 8:20. Transmission and reflection spectroscopy have been used for determining optical characteristics of the film.