Liquid electrolyte-free electrochemical oxidation of GaN surface using a solid polymer electrolyte toward electrochemical mechanical polishing

Gallium nitride and related materials possess advantageous physical and electrical characteristics for use in high-power/frequency devices and optoelectronics. However, surface preparation of GaN, such as oxidizing and etching, remains difficult owing to its superior chemical and thermal stability compared to conventional semiconductor materials. Thus, high-temperature treatment or ultraviolet irradiation is required to process the GaN surface. Here, we report a novel electrochemical approach for the oxidization of GaN surface using solid polymer electrolyte (SPE), which provides a room-temperature surface treatment free from liquid electrolyte and UV irradiation. The electrochemical system composed of GaN/SPE/cathode can effectively oxidize the GaN surface (~80 nm, 10 min) in the presence of H2O molecules via a reaction with hydroxyl radicals (OH) generated on the SPE membrane. While the surface shows rough and porous features after the removal of oxide by dipping in an alkaline solution, post-oxidation polishing using CeO2 particles removes the oxide film to produce a smooth GaN surface, which demonstrates the potential of oxidation/polishing for GaN wafer fabrication processes.