Two-photon spectroscopy ofBexcitons in CdS

Abstract

High-resolution spectra are obtained for the free $A$ and $B$ excitons in CdS by two-photon absorption photoconductivity techniques at 1.8 K. At zero applied magnetic field, spectra are shown which indicate for the first time the presence of anisotropy splitting of the $B(2P)$ exciton states. The first observation of the $B(3P)$ exciton state at $B=0$ T then allows the conclusion that both the effective Rydberg and the anisotropy parameter of the $A$ and $B$ excitons are the same. This further indicates that the $A$ and $B$ valence-band masses are equal. These conclusions are confirmed by the first observation of the Zeeman splitting of the $B(2{P}_{\ifmmode\pm\else\textpm\fi{}1})$ and $B(3{P}_{\ifmmode\pm\else\textpm\fi{}1})$ exciton states at fields up to 10 T. Fine-structure splitting of the $B(2{P}_{+1})$ and $B(2{P}_{\ensuremath{-}1})$ states results from an effective $g$ factor for the $B$ valence band of ${g}_{h}^{B}=0.7\ifmmode\pm\else\textpm\fi{}0.3$.