Faceted sidewall etching of n-GaN on sapphire by photoelectrochemical wet processing

A wet etch process that produces smooth sidewalls aligned with the m-plane ({$11¯00$}) crystal facets of Ga-polar GaN grown on sapphire is demonstrated by combining photo-electrochemical (PEC) treatment with a postprocessing wet etch step. This novel process results in faceted and extremely smooth vertical etched sidewalls. This two-step process consists of a PEC treatment to define the geometry by converting the region to be removed to an oxide, followed by selective wet-chemical removal of the oxide in buffered HF and post-etch immersion in KOH (0.5 M) at 150 °C to smooth the surface and reveal the crystal planes. The dependence of the PEC treatment parameters (optical intensity, solution composition, direct current bias) on the resulting etch rates and morphology has been investigated.