Analysis of IR spectra of thin films such as a-Si:H can yield quantitative compositional information. However, to calculate the integrated absorbances of features in the spectra, multiple internal reflections in the film must be accounted for. In practice, this has been done either by mathematically estimating the degree of multiple reflections or by using substrates designed to eliminate the reflections, typically wedged or roughened c-Si. These techniques are compared on the basis of accuracy and ease of substrate preparation.
Device~luality a,Si:H was deposited by glow discharge simultaneously on a variety of c-Si substrates: double-polished, single-polished (rough side), single-polished (polished side), roughened, and wedged. Correction for multiple reflections in the spectrum of a~qi:H on a double-polished substrate gives the same absorbance as that on a wedged substrate. This confirms the accuracy of the correction for multiple reflections and shows that it is unnecessary to prepare wedged substrates. The transmission spectra of the Si-H peak at 630 cm -1 are identical for all non-wedged substmtes regardless of surface roughness. Thus, there is no advantage in using deliberately roughened substrates and no need for double-polished substrates.