Free excitons in cubic CdS films

Cubic CdS layers have been epitaxially grown on (001) GaAs substrates by a low-pressure metalorganic chemical vapor deposition technique, and their free exciton states have been studied by means of modulated reflectance spectroscopy. Light-hole and heavy-hole excitons are split by biaxial compressive strains in the 2 μm CdS films. It has been found that a sharp photoluminescence (PL) appears at low temperatures and the PL energy coincides with the light-hole exciton energy. Two peaks in the PL excitation spectrum agree well with the light-hole and heavy-hole exciton energies. The free exciton energy has been determined for cubic CdS films on GaAs substrates.