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.
Tin doped indium oxide (ITO) thin films are being used extensively as transparent conductors in several applications. In the present communication, we report the electrical transport in DC magnetron sputtered ITO thin films in low temperatures (25-300 K). The low temperature Hall effect and resistivity measurements reveal that the ITO thin films are moderately dis-ordered (k f l~1) and degenerate semiconductor. The transport of charge carriers in these disordered ITO thin films takes place via the de-localized states. The disorder effects lead to the well-known metal-insulator transition; this transition is observed at 110 K in ITO thin films. The metalinsulator behaviour is explained by the quantum correction to the conductivity (QCC); this approach is based on the quantum-mechanical interference effects in the disordered systems. The insulating behaviour is attributed to the combined effect of the weak localization and the electron-electron interactions.
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