Polarity and dislocation dependence study of photo-electrochemical wet etching on GaN was carried out on lateral epitaxial overgrown non-polar (11▪0)a-GaN/(1¯1▪2)r-plane sapphire substrate. This LEO non-polar GaN sample had low dislocation density Ga- and N-faces exposed horizontally in opposite directions, which could be exposed to identical etching conditions for both polarity and dislocation dependence study. It was observed that N-face GaN was essentially much chemically active than Ga-face GaN, which exhibited hexagonal pyramids with {10▪¯1} 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 (¯1¯1▪¯2) facet as an etch stop plane both on Ga and N-wing region.

Dislocation- and Crystallographic-Dependent Photo-Electrochemical Wet Etching of Gallium Nitride. Y.Gao, M.D.Craven, J.S.Speck, S.P.DenBaars, E.L.Hu: Applied Physics Letters, 2004, 84[17], 3322-4