Surface passivation and interface reactions induced by hydrogen peroxide treatment of n-type ZnO (0001¯)

X-ray photoemission spectroscopy and electrical measurements have been employed to study O-face (0001¯) n-type ZnO samples treated by hydrogen peroxide (H2O2). A highly resistive and oxygen-rich surface layer is revealed, presumably caused by a high concentration of zinc vacancies and/or adsorbed O2 molecules. As a result, the surface exhibits upward energy band bending (∼0.4 eV) promoting the formation of high barrier Schottky contacts and suppressing the surface leakage current. Furthermore, after Pd deposition an enhanced formation of PdO is found at the Pd/ZnO interface for the H2O2-treated samples, and this is also expected to increase the resulting Schottky barrier height (∼0.6 eV), which yields up to seven orders of magnitude in current rectification between forward and reverse bias voltage.