Influence of thickness on the optical properties of vacuum-deposited a-Si:H films

The influence of the thickness of the a-Si : H film on its optical properties was studied using spectrophotometric measurements of the film transmittance and reflectance in the wavelength range 200-3000 nm. Both the refractive index and the absorption coefficient were found to increase as the film thickness increased and the absorption edge shifted to lower energies. Both the optical energy gap, Eg, and Urbach parameter values, E0, decreased with increasing thickness. This decrease in Eg and E0 was slow for thicknesses above 400 nm.