Electronic properties of ZnO

Abstract

Hall effect measurements on doped, n-type single-crystals of ZnO have yielded: a density-of-states mass of 0.5 m, a shallow donor ionization energy of 0.05 eV, and the temperature dependence of mobility. An effective mass of 0.27 m, is derived from the donor binding energy. It is used in the computation of the optical-mode scattering, which together with some acoustical-mode scattering, fits the mobility data. Thermoelectric power measurements show the presence of a large phonon-drag ( Q p) contribution. The Q p saturation effect yields an effective inertial mass of 0.07 m, and it is shown that it is approximately isotropic. Magnetoresistance measurements show that there must be at least 12 valleys in the ZnO conduction band and that the valleys are not greatly anisotropic. The small inertial mass is compatible with the density-of-states mass and the 12 valleys of small anisotropy; however, the donor binding energy and the optical-mode scattering both seem to require an effective mass larger by a factor of 4. A tentative model is suggested which might resolve this difficulty.