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Time-resolved threshold switching characteristics including transient parameters such as delay time and holding voltage are reported for a nanoscale GeTe6 Ovonic threshold switching (OTS) device. The voltage dependence of the threshold switching process has been studied, revealing switching in less than 5 ns in the fastest case. A constant holding voltage is observed for the different voltage pulses applied, which is an indicative for a stable on state in the amorphous phase. In addition, the potential of GeTe6 devices as OTS selectors is validated.

We report an inelastic (Raman) light scattering study on bulk crystalline GeTe (c-GeTe) and amorphous GeTe (a-GeTe) thin films and found to show pronounced similarities in local structure between the two states. In c-GeTe, the observed Raman modes represent the Ge atoms are in three different environments, namely, tetrahedral, distorted, and defective octahedral sites. On the other hand, in a-GeTe, Raman spectrum reveals Ge sites in tetrahedral and defective octahedral environment. We suggest that the structure of c-GeTe consists of highly distorted as well as defective Ge sites, which leads to the large concentration of intrinsic defects (vacancies). These random defects would act as topological disorder in the lattice and cause the bands to develop tails at the band edges, a continuum of localized levels appearing in the gap. The present study deepens the understanding of the local atomic structure, influence of defects and its close relation to the phase-change mechanism.

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