Influence of texture on the absorption threshold of LPCVD silicon films

Polycrystalline silicon films were chemically vapor deposited on oxidised s ilicon and quartz substrates from SiH4 decomposition in a conventional reac tor at 230 mTorr and at temperatures of 550, 610 and 700 degreesC. Samples were characterized by optical transmission and atomic force microscopy meas urements, The optical properties of these films were studied within a two-b and model proposed by A. Forouhi and I. Bloomer (Phys. Rev. B34, 7018 (1986 )) that is able to provide an approximate picture of the energy distributio n of the density of electronic states. It was found that this model describ es satisfactorily the optical properties of films near the absorption thres hold. It was also shown that the energy distribution of the density of stat es is influenced by crystallization and film texture. Electronic transition s at different points of the Brillouin zone dominate the optical properties . Thus, transitions near the K point of the Brillouin zone dominate the opt ical properties of films grown at 610 degreesC, while for films grown at 70 0 degreesC the dominant role is played by transitions at the X, K and L poi nt.