Theoretical Study of a Two-dimensional Electron Gas in Wurtzite ZnO/MgZnO Heterostructures and Comparison with Experiment

The effect of polarization on a two-dimensional electron gas in the ZnO/MgZnO heterostructure were investigated by using an effective mass theory. The O-face MgZnO/ZnO structure is shown to have a larger sheet carrier density than the Zn-face structure. This can be explained by the fact that, in the case of the O-face, the ZnO layer is under tensile strain, and the strain-induced polarization is parallel to the orientation of the spontaneous polarization. The calculated results for the O-face agree well with the experiment. Also, the contribution of additional donor impurities on the electron sheet concentration is shown to be less effective when the Mg mole fraction is large.