Photostructural changes in bulk amorphous Ge 1−xSn xSe 2

Abstract

Optical absorption studies have been performed on bulk amorphous Ge 1−xSn xSe 2 (0.00 ≤ × ≤ 0.60). As the Sn concentration is increased, the optical band gap (Eg at α = 150 cm −1) is observed to decrease from 2.11 eV at x = 0.00 to 1.65 eV at x = 0.60, except for a slight rise at x = 0.25 attributed to the fragmentation of the molecular cluster. Photo-induced shifts in the optical band gap indicate that the tathogen may be important in determining the direction of the shift. For GeSe 2 only ohoto-darkening is observed but for samples containing Sn both photodarkening and photobleaching are observed. Changes in the band gap, the cluster size, and the location of the Sn atoms as x is increased preclude the identification of specific mechanisms with specific shifts in the band gap. The shift in the band gap is determined by which of the structural changes is favored under the conditions of illumination.