Role of Photoelectrochemical Oxidation in Enabling High-Efficiency Polishing of Gallium Nitride

Photoelectrochemical (PEC) oxidation is currently employed to improve the removal rates of surface polishing methods applied to gallium nitride (GaN) wafers, such as PEC mechanical polishing (PECMP) and PEC catalyst-referred etching (PEC-CARE). The use of PEC along with these methods has successfully achieved removal rates as high as 720 nm h(-1) while still ensuring the highly ordered step-and-terrace structures generated by the same methods when PEC-oxidation is not employed. However, the atomic-scale phenomena induced by PEC oxidation to assist the polishing process of GaN surfaces remain unclear. To address such a question, this study investigates the role of PEC oxidation during CARE as an example. The results demonstrate that PEC oxidation selectively occurs at the step edge and advances through the GaN (0001) surface laterally rather than in the depth direction, thus enabling high-speed polishing and resulting in a highly ordered surface, both crystallographically and geometrically.