Exciton Effects in the Electroabsorption of Cadmium Sulfide

Optical-absorption and electroabsorption spectra of cadmium sulfide have been measured in the vicinity of the fundamental absorption edge at temperatures from 4.2-300^∘{}K, using thin-film samples. The optical-absorption spectra show the features characteristic of the single-crystal exciton spectrum. Comparison of the electroabsorption with optical absorption for applied fields up to 5×{}10⁴ V cm^-1 shows that exciton states are responsible for the electroabsorption. No electroabsorption structure which can be associated unambiguously with band-to-band transitions can be seen for photon energies in the range of 2.4-2.7 eV. Effects associated with bound excitons dominate the electroabsorption at 77^∘{}K and below.