Comparative study of atomic arrangements in equiatomic GeSe and GeTe films before and after crystallization

EXAFS analysis is performed on equiatomic GeSe and GeTe films to elucidate changes in the local atomic environments induced by crystallization. It reveals for both the films that the 4:2 configuration dominates in their as-deposited amorphous state. In their crystallized state, however, the 3:3 configuration prevails together with quasi-crystalline Ge clusters. The two chalcogenide films exhibit very similar characteristics such as hidden glass transition phenomenon during heating, dominance of the 3:3 configuration in their melt state, decreased optical bandgap upon crystallization, and reduced temperature dependence of electrical conduction accompanied with crystallization. These common properties are partly attributed to the structural changes identified through our EXAFS analysis. In particular, their previously reported non-ohmic current-voltage behaviors associated with the phase switching and the threshold switching are explained in terms of the local structural information. The special phase-change properties of the equiatomic GeSe film is explicated by its amorphous structure.