Reproducibility of the Optical Absorption Edge in Amorphous GeS2

Herein, poor reproducibility of optical absorption edges in GeS2 glasses and films is seen. Reported spectral positions of the absorption edge in melt-quenched glasses spread over approximate to 0.2 eV at & hstrok;omega approximate to 3 eV. In deposited films, the edge red-shifts to & hstrok;omega approximate to 2.5 eV showing wider variations of approximate to 1 eV. This work considers plausible reasons of such low, spectral reproducibility, with the aid of ab initio molecular orbital analyses of Ge-S clusters and known insights on optical gaps, electron-spin-resonance signals, and structural data. The variation in the glass is likely to be governed by several factors including compositional fluctuation, edge/corner-shared configurations, wrong bonds, and intimate valence-alternation pairs. The conspicuous red-shift in the films seems to be affected also by neutral dangling bonds.