A method was suggested to characterize the defect density of a given GaN film, through anodic etching. It was noted that oxalic acid etched GaN at room temperature and pressure in an electrolytic cell. The etching was suggested to proceed by attacking points at which planar defects and threading dislocations terminated on the GaN surface. The effect of varying electrolysis voltage upon the etch-pit density of the porous GaN thus formed was investigated. Etch-pit densities of the order of 4 x 1010/cm2 were measured. The use of etch-pit density to estimate the defect density of a given GaN film was considered.
Gallium Nitride - Method of Defect Characterization by Wet Oxidation in an Oxalic Acid Electrolytic Cell. S.P.Sundararajan, D.Crouse, Y.H.Lo: Journal of Vacuum Science & Technology B, 2002, 20, 1339-41