Effect of copper on the local structure of GeSe₂Cu_x probed by Raman spectroscopy

Glassy GeSe₂ is known to exhibit photodarkening that is extinguished by the presence of copper. Bulk glasses of GeSe₂Cu _x (0<x<0.16), prepared by melt-quenching, were studied by Raman spectroscopy to ascertain the effect of copper on the local structure of the glass. Decreases were observed in relative areas of the A_1c (218 cm^-1) and Ge-Ge (178 cm^-1) peaks relative to the A ₁ (201 cm^-1) for compositions of less than x=0.05 copper but changed very little at higher compositions. The position of the A ₁ and A_1c peaks decreased by 2 cm^-1 in low copper compositions. The density of the samples also increased sharply below x=0.05 and more gradually above x=0.05. The copper is seen as affecting the defects (Ge-Ge bonds) in the stoichiometric germanium-selenium glass but not affecting the tetrahedral Ge(Se_1/2)₄ chains.