Selective etching of GaN polar surface in potassium hydroxide solution studied by x-ray photoelectron spectroscopy

Etching characteristics of nondoped GaN films with the polar surface in KOH solution have been investigated. It is confirmed that the continuous etching in KOH solution takes place only for the GaN films with N-face (−c) polarity independent of the deposition method and growth condition. It is found by x-ray photoelectron spectroscopy (XPS) analysis for the Ga face (+c) and N-face (−c) GaN films that the atomic composition of the +c surface is not changed before and after dipping in KOH solution and that on the other hand, the amount of oxygen (oxide) on the −c surface is significantly decreased by the etching. It is also found that the band bending increases by −0.4±0.2 and 0.6±0.2 eV for the +c and −c surfaces after etching, respectively. This is discussed in terms of the surface chemistry. Based on the XPS result, the selective etching of the GaN polar surface is pointed out to originate from bonding configuration of nitrogen at the surface.