Crystal growth, electron structure and photo induced optical changes in novel AgxGaxGe1-xSe2 (x=0.333, 0.250, 0.200, 0.167) crystals

Quaternary single crystals AgxGaxGe1-xSe2 (x = 0.333, 0.250, 0.200, and 0.167) have been grown by the two-zone Bridgman method. X-ray diffraction analysis has revealed that all the four compounds are crystallized in the noncentrosymmetric orthorhombic space group Fdd2. Position of constituent atoms in the unit cells of the AgxGaxGe1-xSe2 single crystals have been determined. X-ray photoelectron core-level and valence-band spectra for pristine and Ar+ ion-irradiated surfaces of the single crystals under consideration have been measured. It has been established that the AgxGaxGe1-xSe2 single crystals are very sensitive to Ar+ ion-irradiation. In particular, bombardment of the single-crystal surfaces with energy of 3.0 key during 5 min at an ion current density of 14 mu A/cm(2) has induced significant modification in top surface layers leading to complete elimination of Ag atoms in the layers. Furthermore, for all four AgxGaxGe1-xSe2 single crystals, the charge states of Ag, Ga, and Ge atoms do not alter when varying the x value, whilst the negative charge of selenium atoms slightly decreases with decreasing x value. All the crystals show substantial photo induced changes of absorption under influence of 808 nm 0.8 W cw laser. (C) 2012 Elsevier B.V. All rights reserved.