Estimation of amorphous silicon thin film density by optical methods

Abstract

Due to lack of long-range ordering, the density of amorphous silicon is lower than in its crystalline form. By hydrogenation of material, the density difference becomes larger. In order to study the effect quantitatively, a series of thin amorphous hydrogenated silicon films, with variation in hydrogen to silicon ratio from 6 to 31 at%, deposited by magnetron sputtering, was examined by UV–visible–IR spectroscopy and nuclear methods. The film density of deposited films was estimated using three different approaches. In the first one, the density was estimated by using effective medium approximation (EMA) analysis of a long wavelength dielectric function. In particular, the basic and modified Maxwell–Garnett models were tested. The second set of values for density was obtained by analysis of stretching vibrations of Si–H bonds in the IR part of the spectrum, by using an earlier published method. The results of all methods applied are compared and their plausibility is discussed.