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  • Title: Direct observation of metal-insulator transition in single-crystalline germanium telluride nanowire memory devices prior to amorphization.
    Author: Nukala P, Agarwal R, Qian X, Jang MH, Dhara S, Kumar K, Johnson AT, Li J, Agarwal R.
    Journal: Nano Lett; 2014; 14(4):2201-9. PubMed ID: 24628625.
    Abstract:
    Structural defects and their dynamics play an important role in controlling the behavior of phase-change materials (PCM) used in low-power nonvolatile memory devices. However, not much is known about the influence of disorder on the electronic properties of crystalline PCM prior to a structural phase-change. Here, we show that the application of voltage pulses to single-crystalline GeTe nanowire memory devices introduces structural disorder in the form of dislocations and antiphase boundaries (APB). The dynamic evolution and pile-up of APBs increases disorder at a local region of the nanowire, which electronically transforms it from a metal to a dirty metal to an insulator, while still retaining single-crystalline long-range order. We also observe that close to this metal-insulator transition, precise control over the applied voltage is required to create an insulating state; otherwise the system ends up in a more disordered amorphous phase suggesting the role of electronic instabilities during the structural phase-change.
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