Abstract
We use the dispersion of the refractive index of subgap light to determine the main parameters of the band structure of thin films of semiconductors. By making a semiempirical calculation of the effect of the final width of the valence and conduction bands, we obtain a variation in the refractive index n(E) with the light energy E, which goes one order beyond the simple two-level one-oscillator formula. By comparison with the experimental transmission curve, we show that it is possible to obtain, with a simple commercial spectrometer, the distance E M between the centres of gravity of the valence and conduction bands and also an estimate of the widths Δ of the bands. We have applied this method to a series of thin films of hydrogenated amorphous silicon and carbonated alloys.
