Excellent potential of photo-electrochemical etching for fabricating high-aspect-ratio deep trenches in gallium nitride

Photo-electrochemical (PEC) etching was used to fabricate deep trench structures in a GaN-on-GaN epilayer grown on n-GaN substrates. A 50-nm-thick layer of Ti used for an etching mask was not removed even after etching to a depth of > 30 mu m. The width of the side etching was less than 1 mu m with high accuracy. The aspect ratio (depth/width) of a 3.3-mu m-wide trench with a PEC etching depth of 24.3 mu m was 7.3. These results demonstrate the excellent potential of PEC etching for fabricating deep trenches in vertical GaN devices. (C) 2018 The Japan Society of Applied Physics