Facets evolution and surface electrical properties of nonpolar m-plane ZnO thin films

ZnO thin films have been grown along the nonpolar [101¯0] direction by metal organic vapor phase epitaxy. The ZnO (101¯0) surface develops well defined facets. The orientation of the topographic normals reveals that the inclination angle of the facets increases as thicker films are considered, attaining a maximum value of about 28.4°. This angle corresponds to {101¯1}- and {101¯1¯}-type facets. The origin of this faceting is discussed in terms of thermodynamic stability and kinetics arguments. The surface electrical properties of the facets have been studied by Kelvin probe microscopy, showing that the surface has different contact potential domains that alternate along the polar [0001] direction.