Electron transport in high quality undoped ZnO film grown by plasma-assisted molecular beam epitaxy

High quality ZnO films were grown on c-plane sapphire substrate using low temperature ZnO buffer layer by plasma-assisted molecular beam epitaxy. The film deposited at 720 °C showed the lowest value of full-width at half maximum for the symmetric (0002) diffraction peak of about 86 arcsec. The highest electron mobility in the films was about 103-105 cm²/V s. From temperature-dependent Hall effect measurements, the mobility strongly depends on the dislocation density at low temperature region and the polar optical phonon scattering at high temperature, respectively. Moreover, by obtaining the activation energy of the shallow donors, it was supposed that hydrogen was source of n-type conductivity in as-grown ZnO films.