Stabilization of ZnO polar plane with charged surface nanodefects

Abstract

Based on in situ scanning probe microscopy/spectroscopy, this study investigates the stabilization of Zn-terminated ZnO polar plane using surface defects. O-terminated surface defects on a nanometer scale, which have two morphologies, i.e., hexagonal cavities and small pits, are observed at the submonolayer depth on the (0001)-Zn surface by applying medium-energy ${\text{Ar}}^{+}$ bombardment (2.5 keV) at a high temperature $(850\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C})$. Experimental results indicate that the local electronic structure of O-terminated surface defects exhibits upward band bending with respect to the Zn-terminated surface, which is consistent with the observations made using Kevin probe microscopy, in which the ZnO polar surface has a locally reversed electrostatic field. Moreover, pair-distribution analysis indicates that the O-terminated surface defects with diameters below 0.9 nm are charged with one electron per pit, thus helping to compensate for the internal polarization.