Optical Spectra and Band Structure of As₂Se₃

The optical properties of the layer material As 2 Se 3 at low temperature are presented in the energy range between 1 and 9 eV for polarization of light parallel to the three crystal axes including the stacking direction of the layers. The results are compared with a band structure calculated by means of a semi‐empirical tight‐binding model. It turns out that in As 2 Se 3 no lone‐pair bands exist like for instance in Se. In particular there is no gap between bonding and non bonding p states. The direct gap occurs at the point Γ. Some of the upper valence bands near Γ show considerable splitting due to interlayer interaction. Nevertheless selection rules and the dependence of the optical spectra on the polarization of light are essentially determined by the symmetry of the single layer.