Quantum-interference transport through surface layers of indium-doped ZnO nanowires

We have fabricated indium-doped ZnO (IZO) nanowires (NWs) and carried out 4-probe electrical-transport measurements at low temperatures. The NWs reveal charge conduction behavior characteristic of disordered metals. In addition to the $T$ dependence of resistance $R$, we have measured the magnetoresistances (MR) in perpendicular and parallel magnetic fields. Our $R(T)$ and MR data in different $T$ intervals are consistent with the theoretical predictions of the one- (1D), two- (2D) or three-dimensional (3D) weak-localization (WL) and the electron-electron interaction (EEI) effects. In particular, a few dimensionality crossovers in the two effects are observed. These crossover phenomena are consistent with the model of a "core-shell-like structure" in individual IZO NWs, where an outer shell of a thickness $t$ ($\simeq$ 15-17 nm) is responsible for the quantum-interference transport. In the WL effect, as the electron dephasing length $L_\phi$ gradually decreases with increasing $T$ from the lowest measurement temperatures, a 1D-to-2D dimensionality crossover takes place around a characteristic temperature where $L_\phi$ approximately equals $d$, an effective NW diameter which is slightly smaller than the geometric diameter. As $T$ further increases, a 2D-to-3D dimensionality crossover occurs around another characteristic temperature where $L_\phi$ approximately equals $t$ ($< d$). In the EEI effect, a 2D-to-3D dimensionality crossover takes place when the thermal diffusion length $L_T$ progressively decreases with increasing $T$ and approaches $t$. However, a crossover to the 1D EEI effect is not seen because $L_T < d$ even at $T$ = 1 K in our IZO NWs. Furthermore, we explain the various inelastic electron scattering processes which govern $L_\phi$. This work indicates that the surface-related conduction processes are essential to doped semiconductor nanostructures.