Modulated photoconductivity method for investigation of band gap states distribution in silicon-based thin films

It has been demonstrated that the well known modulated photocurrent technique can be modified to escape imperfect data in intrinsic parameters of amorphous and microcrystalline silicon films and to simplify measurements of the density of localized states distribution in the band gaps of these semiconductors. The information on the density-of-states distribution can be extracted from temperature dependence measurements of the constant and modulated components of the photoconductivity in the film illuminated by the light modulated with some selected frequencies. The modified method has been applied to microcrystalline hydrogenated silicon films with n- and p-type conduction. The study has demonstrated that the tail of the density-of-states distribution near the valence band of microcrystalline hydrogenated silicon is less steep than that near the conduction band.