Electronic structure ofTl3AsSe3

An experimental and theoretical investigation of the electronic structure of a ternary semiconductor, ${\mathrm{Tl}}_3$As${\mathrm{Se}}_3$, is reported. The total valence-band density of states has been measured by x-ray photoelectron spectroscopy (XPS). A simple prescription, utilizing atomic term values, is suggested for identifying the major features in an XPS spectrum and is applied to this ${\mathrm{Tl}}_3$As${\mathrm{Se}}_3$ spectrum. In addition, detailed tight-binding band-structure calculations, based on universal parameters, were performed, and a computationally novel scheme was employed for obtaining the theoretical density of states in good agreement with the experimental spectrum. The valence-band density of states has three main characteristics. The Se $4p$ and Tl $6s$ states contribute to three peaks in a 7-eV region immediately below the valence-band maximum. The As $4s$ states and Se $4p$ states combine to give a shoulder 10 eV below the top of the valence band. The Se $4s$ bands occur where they are obscured by the intense Tl $5d$ core levels.