Ultraviolet Reflection Spectrum of Cubic CdS

Abstract

The normal-incidence reflection spectrum of cubic CdS has been measured for photon energies between 2 and 22 eV. The samples were prepared by epitaxial deposition on the {1¯11} "As face" of GaAs. The lowest direct absorption edge produces a reflection peak at 2.50 eV at room temperature. The $E_1$ peak (at 5.49 eV) does not show the splitting characteristic of hexagonal (wurtzite-type) material. The $F_1$ peak previously reported for wurtzite-type CdS at 7.12 eV is absent in cubic CdS. All other features of the reflection spectra of cubic and hexagonal CdS are very similar. The mixed cubic-hexagonal nature of CdS films deposited on the {1¯11} "P face" of GaP is easily detected with the help of the reflection spectrum: The split component of the $E_1$ peak and the $F_1$ peak appear less intensely than in pure hexagonal CdS. The preparation and epitaxy of cubic and hexagonal CdS films are described and interpreted.