Electronic structure and photoelectrical properties of Ag2In2SiSe6 and Ag2In2GeSe6

Abstract

High-quality Ag2In2SiSe6 and Ag2In2GeSe6 single crystals have been successfully grown by the vertical Bridgman–Stockbarger method and the horizontal gradient freeze technique, respectively. For pristine and Ar+ ion-irradiated surfaces of the single crystals under study, X-ray photoelectron core-level and valence-band spectra have been measured. Results of these studies allow for concluding that the Ag2In2SiSe6 and Ag2In2GeSe6 single crystal surfaces are sensitive with respect to Ar+ ion-irradiation. In particular, Ar+ ion-bombardment with energy of 3.0keV during 5min at an ion current density of 14μA/cm2 has induced some modification in top surface layers leading to an increase of content of In atoms in the layers. Comparison on a common energy scale of the X-ray emission Se Kβ2 bands representing energy distribution of the Se 4p states and the X-ray photoelectron valence-band spectra reveal that the main contribution of the valence Se p states occur in the upper portion of the valence band, with also their significant contributions in other valence band regions of the Ag2In2SiSe6 and Ag2In2GeSe6 single crystals. In addition, for the single crystals under consideration, temperature dependences of specific dark conductivity and spectral distributions of photoconductivity have been explored. It has been established that the Ag2In2SiSe6 and Ag2In2GeSe6 single crystals are high-resistance semiconductors with value of the specific electrical conductivity σ≈1.67×10–9Ω–1сm–1 (at Т=300K). The both compounds are materials with p-type conductivity.