Order-disorder phase transition in an amorphous GeSbTe compound

Conductance noise measurements on amorphous films of GeSbTe reveal a structural phase transition driven by temperature. Measurements are performed on samples that were first densified by multiple heat-treatment cycles. In the heavily densified regime, varying the film temperature changed the resistance in a systematic and reproducible way. Monitoring the conductance noise of the sample during temperature cycles, revealed a reversible process. The power spectrum and magnitude of the conductance-noise, measured over the 295–330 K temperature range, exhibited changes that are characteristics of a phase transition. The phases defined in the transition are distinguished by the spectral form and magnitude of their low-frequency fluctuations. This is argued to be a structural order-disorder transition. Raman spectroscopy shows the presence of Ge_xTe_y clusters, confirming previous reports of their high density in the amorphous material, comparable to the crystalline phase. The possible role that these structural motifs play in the observed transport features is discussed.