Anodic oxidation of gallium nitride

The anodic oxidation of n-type GaN (carrier concentration 4.6 × 1018 cm−3) under laboratory illumination at a constant current density of 5 mA cm−2 in sodium tungstate electrolyte is examined by high resolution microscopy and surface analysis. The GaN, deposited as a thin layer by molecular beam epitaxy, had an initially faceted surface. Anodic oxidation gives rise to local growth of an amorphous Ga2O3-based reaction product, often, but not exclusively, located in the vicinity of troughs formed by intersecting facets. At these regions dislocations in the GaN intersect the surface. The product is non-uniform in thickness and morphology, with pore-like features. With prolonged anodic treatment, local oxidation progresses as channels, which eventually reach the base of the GaN layer, leaving a porous skeleton. The formation of a uniform and compact film material on GaN is considered to be impeded by generation of nitrogen from the anodic reaction, with the strength of the Ga–N bonding focusing oxidation on regions of increased impurity, non-stoichiometry or defect concentration.