Local structure of technologically modified g-GeS2: resonant Raman and absorption edge spectroscopy combined with ab initio calculations

We have used resonant Raman and absorption edge spectroscopy together with first-principle calculations in order to study the structure of GeS₂ glasses (g-GeS₂). The glasses were prepared under different melt temperatures and cooling rates, which are shown to significantly influence the g-GeS₂ structure at the nano-scale. The combined use of Raman spectroscopy and ab initio calculations reveals the origin of the molecular level electronic structure and its connection to the interesting technological features of the g-GeS₂. Local structure within the glasses is discussed in terms of atomic Ge _n S _m clusters. The band gaps computed for these clusters and their correlation to the experimental band gaps and the possible formation of band tail states are also discussed.