Light scattering and ellipsometric studies at and below energy gap: polycrystalline calcium and strontium thiogallates

An approach based on peculiar angles is considered in relation with the problem of restoration of the dielectric function from ellipsometric measurements at and below energy gap on polycrystalline materials with macroscopic roughness. It is shown that at least for macroscopically and mildly rough surfaces, scattering changes only the amplitude diminution while the phase remains unchanged. This offers a possibility to restore the ellipsometric angles unperturbed by scattering provided that the parameters of surface distribution are known. The ellipsometric data on polycrystalline calcium and strontium thiogallates are briefly overviewed in connection with the performed analysis. The results of comparison show that both multiple scattering and overlayer-type effects can be involved in the transient region between diffraction and geometric optics.