THE INFLUENCE OF THICKNESS AND INDEX INHOMOGENEITIES ON THE TRANSMISSION OF SEMICONDUCTOR THIN-FILMS

In order to analyse spectrophotometric measurements, an analytical formulation of the transmission of films with thickness or index imhomogeneities is presented. The experimental resolution is taken into account. A numerical method is presented and applied to sputtered cadmium sulphide films and hydrogenated amorphous silicon films produced by glow discharge. The method allows us to compute the mean thickness fluctuation or the mean index fluctuation and to increase the accuracy in the determination of the optical constants and thickness. The refraction index and thickness are obtained lo within less than 1%. The computation method also allows us to decrease strongly the large uncertainty in the determination of the absorption coefficient in the immediate neighbourhood of the fundamental band edge.