“…The wet chemical treatments of GaN and AlGaN surfaces have been intensively studied by means of X-ray photoelectron spectroscopy (XPS). Etchants such as HF [8][9][10], buffered HF [8,11], HCl [8][9][10]12], HNO 3 [8], H 2 SO 4 [8], KOH [9], NaOH [11,12], and NH 4 OH [12][13][14], have been reported to reduce or modify the surface contamination. A recent study by Prabhakaran et al [13] has indicated that 1:10 NH 4 OH:H 2 O etch predominantly removes gallium oxides (Ga 2 O 3 ) from the GaN surface.…”