“…Therefore, reactive-ion etching and inductively coupled plasma (ICP) methods have been widely used for mesa isolation etching for p-n diodes, 1,2) lateral Schottky barrier diodes (SBDs), HEMTs, 3,4) bipolar transistors, 5,6) and laser diodes, 7,8) and the gate recess etching of AlGaN/GaN HEMTs, [9][10][11][12][13][14][15][16] Although ICP is widely used for the etching of GaN, plasma-induced damage is a serious concern in terms of device stability and reliability. [17][18][19][20][21] On the other hand, the PEC etching is a basically damage-less etching system because it is a plasma-free process. In the case of a GaN layer on a sapphire substrate, the PEC etching formed a large number of whiskers due to large dislocation-density.…”