Electron transport in ZnO thin films

TL;DR

This study investigates electron transport in epitaxial ZnO thin films using experimental Hall-effect measurements and theoretical calculations, revealing unique mobility behavior linked to electron-plasmon interactions.

Contribution

It combines experimental data with theoretical modeling to analyze mobility limits and temperature dependence in ZnO thin films, highlighting unusual mobility phenomena.

Findings

Mobility at intermediate carrier concentrations is unexpectedly lower.

Theoretical calculations align well with experimental mobility data.

Electron-plasmon interactions explain the mobility anomaly.

Abstract

Epitaxial, n-type ZnO films grown by a laser molecular-beam epitaxy method were investigated by the temperature-dependent Hall-effect technique. The 300-K carrier concentration and mobility were about $n_s \sim 10^{16}$ cm$^{-3}$ and 440 cm$^{2}$/Vs, respectively. Transport characteristics are calculated by solving the Boltzmann transport equation using a variational method. Mobility limit of 430 cm$^{2}$/Vs was calculated at 300 K. The temperature dependence of the mobility for an undoped film is calculated and agrees favorably well with experimental data if physical parameters are chosen so as to approach to those. In the experimental `mobility vs concentration' curve, unusual phenomenon was observed, i.e., mobilities at $n_s \sim 5\times$ 10$^{18}$ cm$^{-3}$ are significantly smaller than those at higher densities above $\sim 10^{20}$ cm$^{-3}$. It is qualitatively explained in terms of electron-plasmon interaction.