Depth profiling of nonuniform optical absorption in thin films: Application to hydrogenated amorphous silicon

The amplitude of interference fringes in optical absorption spectra for thin films has been analyzed in the range of low absorption coefficients and was found to be related to a depth profile of absorbers, e.g., defects. This method has been applied to the subband-gap optical absorption spectra measured by photothermal deflection spectroscopy for hydrogenated amorphous silicon thin films. It is shown that the analysis of interference fringes provides unique information about surface and interface defects in this material.