Efficient Wet Etching of GaN (0001) Substrate with Subsurface Damage Layer

Photoenhanced chemical (PEC) etching is applicable for processing an n-GaN (0001) surface rapidly. In this process, the surface oxidation is enhanced by photo-generated holes and the resulting oxide can dissolve into solutions. In current work, we conduct bias-assisted PEC etching in a KOH solution with a positively biased wafer, to remove the crystallographically highly damaged layer. The employed substrate was mechanically polished with diamond slurry of sub-micrometer particle size. Without the positive bias, the rate of PEC etching was quite low because the photogenerated holes were quickly depleted by the recombination process at the crystallographic defects and they could not contribute to the oxidation. On the other hand, in the case where the bias was applied, the photogenerated holes and electrons are separated forcibly in the band-bended surface, which effectively contributed to surface oxidation. As a result, a high removal rate was realized even on the damaged surface.