Electron transport in ZnO thin films

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 ns ∼ 1016 cm-3 and 440 cm2 V s, respectively. Transport characteristics are calculated by solving the Boltzmann transport equation using a variational method. Mobility limit of 430 cm2 V s 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 those. In the experimental "mobility versus concentration" curve, unusual phenomenon was observed, i.e., mobilities at ns ∼5× 1018 cm-3 are significantly smaller than those at higher densities above ∼ 1020 cm-3. It is qualitatively explained in terms of electron-plasmon interaction.