Giant improvement in the rectifying performance of oxidized Schottky contacts to ZnO

The rectifying performance of platinum, palladium, and iridium Schottky contacts on ZnO(0001) surfaces was dramatically improved by their deliberate in-situ oxidation using an O2:Ar rf plasma during fabrication. For example, oxidized Pt Schottky contacts exhibited current rectification of 12 orders-of-magnitude, effective barrier heights of up to 1.30 eV, and stable high-temperature operation at 180 °C, compared to the ohmic behavior (i.e., zero rectification/barrier height) of unoxidized contacts. Oxidized Pd and Ir Schottky contacts also showed similar dramatic improvements compared to their plain metal counterparts. These very large performance gains are attributed to the presence of active oxygen species during Schottky contact formation that produces the following beneficial effects: (1) the removal of the hydroxyl-induced surface potential well and associated electron accumulation layer, (2) the passivation of interfacial oxygen vacancies, and (3) an increase in the work function and electronegativi...