Influence of texture on the absorption threshold of LPCVD silicon films

Polycrystalline silicon films were chemically vapor deposited on oxidised silicon and quartz substrates from SiH4 decomposition in a conventional reactor at 230 mTorr and at temperatures of 550, 610 and 700 °C. Samples were characterized by optical transmission and atomic force microscopy measurements. The optical properties of these films were studied within a two-band model proposed by A. Forouhi and I. Bloomer (Phys. Rev. B34, 7018 (1986)) that is able to provide an approximate picture of the energy distribution of the density of electronic states. It was found that this model describes satisfactorily the optical properties of films near the absorption threshold. It was also shown that the energy distribution of the density of states is uifluenced by crystallization and film texture. Electronic transitions at different points of the Brillouin zone dominate the optical properties. Thus, transitions near the K point of the Brillouin zone dominate the optical properties of films grown at 610 °C, while for films grown at 700 °C the dominant role is played by transitions at the X, K and L point