Chemical etching behaviors of semipolar (11(2)over-bar2) and nonpolar (11(2)over-bar0) gallium nitride films

Abstract

Wet chemical etching using hot KOH and H3PO4 solutions was performed on semipolar (11 (2) over tilde2) and nonpolar (11 (2) over bar0) 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 (11 (2) over bar2) and nonpolar (11 (2) over bar0) GaN thin-films. A second etch step in H3PO4 solution additionally exposed a ((1) over bar(1) over bar2 (2) over bar) 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.