Dislocation- and crystallographic-dependent photoelectrochemical wet etching of gallium nitride

Polarity and dislocation dependence study of photoelectrochemical wet etching on GaN was carried out on lateral epitaxial overgrown nonpolar (112̄0)a-GaN/(11̄02)r-plane sapphire substrate. This LEO nonpolar GaN sample has low dislocation density Ga- and N-faces exposed horizontally in opposite directions, which can be exposed to identical etching conditions for both polarity and dislocation dependence study. It is observed that N-face GaN is essentially much chemically active than Ga-face GaN, which shows the hexagonal pyramids with {101̄1̄} facets on the etched N face. No obvious etching was observed on Ga face in the same etch condition. As for dislocation dependence, the “wing” (low dislocation density) region was etched faster than the “window” (high dislocation density) region. Smooth etched surfaces were formed with the (1̄1̄22̄) facet as an etch stop plane both on Ga and N-wing region.