Dielectric function of cubic and hexagonal CdS in the vacuum ultraviolet region

The dielectric function of cubic CdS films grown epitaxially on InP(110) has been determined by spectroscopic ellipsometry in the photon energy range 4.5–18 eV. Structures in the imaginary part of ε below 9.5 eV are assigned to transitions at critical points of the Brillouin zone and are compared with our measurements on hexagonal CdS performed in the same energy range. Structures in ${\mathrm{\epsilon }}_2$ above 12 eV are assigned to transitions from cadmium 4d and sulfur 3s states into the conduction band.