EXAFS spectroscopic refinement of amorphous structures of evaporation-deposited Ge–Se films

Abstract

EXAFS spectroscopic analysis is employed to elucidate the amorphous structure of evaporation-deposited GexSe100−x (x=30, 49 or 69 in at%) films. The difficulty in the determination of local structure resulting from the similar backscattering amplitude of Ge and Se atoms has been overcome through comparative analysis of film specimens subjected to controlled heat treatment. Our results indicate that the 4(Ge):2(Se) structural model, which satisfies the (8−N) rule, is valid for all of the compositions studied. However, the nearly equiatomic Ge49Se51 composition with 4(Ge):2(Se) amorphous structure crystallizes into orthorhombic GeSe crystalline phase with 3(Ge):3(Se) structural arrangements and quasi-crystalline Ge clusters. This significant difference in the local structure of amorphous and crystalline states is a distinctive signature of phase change compositions.