Polarity determination of ZnO thin films by electron holography

The polarity of the ZnO film grown on sapphire using an ultrathin Ga wetting layer has been investigated by electron holography. Spontaneous polarization of the ZnO film leads to localized charges in the surface, which change the potential distribution in the vacuum side of the film. The potential distribution depends on the nature of the bounded charges and change as a function of the distance from the film surface. By studying the dependence of the potential change on the distance from the film surface, the ZnO film with very thin Ga wetting layer is determined to have the [0001] polarity