Photocurrent study on the splitting of the valence band for a CdS single-crystal platelet

A CdS single-crystal platelet has been grown by the sublimation method with a two-step furnace. The platelet sample is yellow, 0.02 mm thick, and has a hexagonal structure of {112¯0} plane perpendicular to the c axis. We have acquired transmission and photocurrent spectra in the range 293 to 33 K. We have found that transmission edges and photocurrent peak positions coincide and that these peaks are due to the transition of electrons from the valence band ${\mathrm{\Gamma }}_9$(A) to the conduction band ${\mathrm{\Gamma }}_7$. The band gap ${\mathit{E}}_{\mathit{g}}$(T) of the platelet sample is found to be 2.552 eV-(5.75×${10}^{\mathrm{-}3}$ eV/K)${\mathit{T}}^2$/(T+3743 K). In the range 293 to 200 K, A-, B-, and C-exciton peaks disappear, whereas in the range 150 to 33 K, B- and C-exciton peaks appear in the photocurrent spectrum.