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Optical properties of hydrogenated amorphous silicon
A detailed study of the optical properties of sputtered hydrogenated amorphous silicon films with varying hydrogen concentration is presented here. The energy dependence of the absorption coefficient is looked into, in detail, from a point of view of understanding the well known Tauc rule and the alternate relations being proposed in recent years. Spectroscopic and bandāstructural models like Wemple-Didomenico and Penn are then utilized to analyze the optical parameters near the bandāgap region of the wavelength spectra. Extensive comparisons of our results are made with those of sputtered aāSi:H films of other workers, glow discharge prepared aāSi:H, chemically vapor deposited and evaporated aāSi, and also crystalline silicon. The similarities in the variation of the optical properties of aāSi:H with increasing hydrogen concentration (or decreasing measurement temperature) to that of crystalline silicon with decreasing measurement temperature lead us to interesting conclusions. Thus, it seems that decreasing disorder (topological or thermal) in aāSi:H is equivalent to decreasing thermal disorder in cāSi, at least as far as the disorderāoptical property relationships are concerned