Comment on ‘‘Depth profiling of nonuniform optical absorption in thin films: Application to hydrogenated amorphous silicon’’ [J. Appl. Phys.70, 5025 (1991)]

Recently, Asano and Stutzmann [J. Appl. Phys. 70, 5025 (1991) and J. Non‐Cryst. Solids 137&138, 623 (1991)] examined the effects of in‐depth nonuniformity on optical absorption spectra of thin films, and reported that the amplitude of interference fringes is related to the depth profile of absorbing centers. They used this effect to analyze photothermal deflection spectra (PDS) of amorphous silicon (a‐Si:H) films to get information on surface and interface defects. In a previous paper [Grillo and De Angelis, J. Non‐Cryst. Solids 114, 750 (1989)], we introduced this technique to study surface/interface defects in a‐Si:H, and gave the analytical formula for calculating explicitly the effect; here we show that application of this equation gives readily the shape of fringes for the cases of interest.