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 300K carrier concentration and mobility were about ns∼1016cm−3 and 440cm2∕Vs, respectively. Transport characteristics are calculated by solving the Boltzmann transport equation using a variational method. Mobility limit of 430cm2∕Vs was calculated at 300K. 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∼5×1018cm−3 are significantly smaller than those at higher densities above ∼1020cm−3. It is qualitatively explained in terms of electron-plasmon interaction.