Studies of the Fine Structure of the Direct Gap of As2Se3 Single Crystals by Electroreflectance

Electroreflectance spectra of As2Se3 single crystals in the energy range between 2 and 2.6 eV are presented for polarization of light parallel and perpendicular to the layer plane. Comparison of the spectra with band structure calculations and bond models reveal a very complicated structure of the energy bands near the direct gap. The direct gap close to 2.20 eV is located near Γ. The spinorbit splitting of the uppermost valence bands of 40 meV is similar to the splitting in trigonal selenium. Optical selection rules and the dependence of the spectra on the orientation of the electric field indicate that the uppermost filled bands arise mainly from the lone pair p‐states of the Se atoms.