Electro-Absorption of CdS Crystals

Measurements of electro-absorption of thin CdS crystals are carried out in the temperature range from 85 to 300°K around the photon energy of the fundamental absorption edge. At 300°K, the spectra show characteristics due to the Urbach-rule edge at low photon energies, while oscillatory behaviors of the spectra are observed at high photon energies. The reduced effective masses assoiated to \(₉\)–\(₇\) and \(₇\)–\(₇\) transitions in CdS are estimated from the dependence of the change in the absorption coefficient on the applied electric field. The spectra of the change at 85°K are concluded to consist of superposition of those related to A 1 - and B 1 -excitons, since the wavelengths at maximum peaks in oscillatory curves of the change of the absorption coefficient at the extrapolated zero-field are consistent to the above exciton wavelengths assigned from results of photoconductivity by Park-Reynolds.