Chemical etching behaviors of semipolar (1122) and nonpolar (1120) gallium nitride films

Wet chemical etching using hot KOH and H₃PO₄ solutions was performed on semipolar (1122) and nonpolar (1120) GaN films grown on sapphire substrates. An alternating KOH/H₃PO₄/KOH etch process was developed to control the orientation of the facets on the thin-film surface. The initial etch step in KOH produced c- and m-plane facets on the surface of both semipolar (1122) and nonpolar (1120) GaN thin-films. A second etch step in H₃PO₄ solution additionally exposed a (1122) plane, which is chemically stable in H₃PO₄ solution. By repeating the chemical etch with KOH solution, the m-plane facets as seen in the original KOH etch step were recovered. The etching methods developed in our work can be used to control the surface morphologies of nonpolar and semipolar GaN-based optoelectronic devices such as light-emitting diodes and solar cells. This journal is