Electron mobility in Gaussian heavily doped ZnO surface quantum wells

Abstract

We present a theory of the low-temperature mobility of electrons in a Gaussian heavily doped zinc oxide surface quantum well (ZnO SFQW), taking into account both surface impurity and surface roughness scattering. The theory also includes strong confinement due to spontaneous polarization charges on the surface of ZnO. The electron distribution is found to be shifted closer to the surface for the O-polar face, while far away therefrom for the Zn-polar one. Accordingly, both scatterings are remarkably enhanced in the former case, while reduced in the latter one. Further, high-temperature Coulomb correlation among the charged impurities at a high density in a sample subjected to thermal treatment is proven to significantly reduce scattering by them. Therefore, in such a sample, surface roughness scattering dominates the electron mobility, while for a sample without thermal treatment, both scatterings are important. Our theory provides a good quantitative explanation of the experimental data on electron transport, in particular, the different carrier-density dependences of the mobilities measured in O-polar face ZnO SFQWs prepared in different ways, by bombardment with H2+ ions and by exposure to He+ ions, which has not been explained so far. © 2008 The American Physical Society.