arXiv subjects

Zhi-Qing Li

Publications and source records attributed to Zhi-Qing Li.

40 records · Page 3Linked to original sources

arXiv2013

Structures, optical properties, and electrical transport processes of SnO$_2$ films with oxygen deficiencies

The structures, optical and electrical transport properties of SnO$_2$ films, fabricated by rf sputtering method at different oxygen partial pressures, were systematically investigated. It has been found that preferred growth orientation of SnO$_2$ film is strongly related to the oxygen partial pressure during deposition, which provides an effective way to tune the surface texture of SnO$_2$ film. All films reveal relatively high transparency in the visible range, and both the transmittance and optical band gap increase with increasing oxygen partial pressure. The temperature dependence of resisitivities was measured from 380 K down to liquid helium temperatures. At temperature above $\sim 80$ K, besides the nearest-neighbor-hopping process, thermal activation processes related to two donor levels ($\sim 30$ and $\sim 100$ meV below the conduction band minimum) of oxygen vacancies are responsible for the charge transport properties. Below $\sim 80$ K, Mott variable-range-hopping conduction process governs the charge transport properties at higher temperatures, while Efros-Shklovskii variable-range-hopping conduction process dominates the transport properties at lower temperatures. Distinct crossover from Mott type to Efros-Shklovskii type variable-range-hopping conduction process at several to a few tens kelvin are observed for all SnO$_2$ films.

cond-mat.mtrl-sci↗

arXiv2012

Electron dephasing in homogeneous and inhomogeneous indium tin oxide thin films

The electron dephasing processes in two-dimensional homogeneous and inhomogeneous indium tin oxide thin films have been investigated in a wide temperature range 0.3--90 K. We found that the small-energy-transfer electron-electron ($e$-$e$) scattering process dominated the dephasing from a few K to several tens K. At higher temperatures, a crossover to the large-energy-transfer $e$-$e$ scattering process was observed. Below about 1--2 K, the dephasing time $τ_φ$ revealed a very weak temperature dependence, which intriguingly scaled approximately with the inverse of the electron diffusion constant $D$, i.e., $τ_φ(T \approx 0.3 \, {\rm K}) \propto 1/D$. Theoretical implications of our results are discussed. The reason why the electron-phonon relaxation rate is negligibly weak in this low-carrier-concentration material is presented.

cond-mat.mes-hall↗

arXiv2011

Electrical conduction processes in ZnO in a wide temperature range 20--500 K

We have investigated the electrical conduction processes in as-grown and thermally cycled ZnO single crystal as well as as-grown ZnO polycrystalline films over the wide temperature range 20--500 K. In the case of ZnO single crystal between 110 and 500 K, two types of thermal activation conduction processes are observed. This is explained in terms of the existence of both shallow donors and intermediately deep donors which are consecutively excited to the conduction band as the temperature increases. By measuring the resistivity $ρ(T)$ of a given single crystal after repeated thermal cycling in vacuum, we demonstrate that oxygen vacancies play an important role in governing the shallow donor concentrations but leave the activation energy ($\simeq27\pm$2 meV) largely intact. In the case of polycrystalline films, two types of thermal activation conduction processes are also observed between $\sim$150 and 500 K. Below $\sim$150 K, we found an additional conduction process due to the nearest-neighbor-hopping conduction mechanism which takes place in the shallow impurity band. As the temperatures further decreases below $\sim$80 K, a crossover to the Mott variable-range-hopping conduction process is observed. Taken together with our previous measurements on $ρ(T)$ of ZnO polycrystalline films in the temperature range 2--100 K [Y. L. Huang {\it et al.}, J. Appl. Phys. \textbf{107}, 063715 (2010)], this work establishes a quite complete picture of the overall electrical conduction mechanisms in the ZnO material from liquid-helium temperatures up to 500 K.

cond-mat.mtrl-sci↗

arXiv2011

Logarithmic temperature dependence of Hall transport in granular metals

We have measured the Hall coefficient $R_H$ and the electrical conductivity $σ$ of a series of ultrathin indium tin oxide films between 2 and 300 K. A robust $R_H$\,$\propto$\,ln$T$ law is observed in a considerably wide temperature range of 2 and $\sim$120 K. This ln$T$ dependence is explained as originated from the electron-electron interaction effect in the presence of granularity, as newly theoretically predicted. Furthermore, we observed a $σ$\,$\propto$\,ln$T$ law from 3 K up to several tens K, which also arose from the Coulomb interaction effect in inhomogeneous systems. These results provide strong experimental supports for the current theoretical concepts for charge transport in granular metals with intergrain tunneling conductivity $g_T$$\gg$1.

cond-mat.mes-hall↗