Etched surface morphology of heteroepitaxial nonpolar (11 2 0) and semipolar (11 2 2) GaN films by photoenhanced chemical wet etching

We investigated how selective wet etching changes the surface morphologies of nonpolar a-plane (11 2 0) and semipolar (11 2 2) GaN films grown on sapphire substrates. Trigonal prisms with various widths are seen on the top surface and the tapered sidewall facet of the a-plane GaN films along the c-axis direction. Inclined trigonal unit cells are observed on the semipolar (11 2 2) GaN films after wet etching. The specific crystallographic planes of (10 1 0), (01 1 0), and (0001) were exposed in common for both the GaN films, indicating that these planes are chemically stable due to atomic bond configurations and smaller density of atoms. Photoenhanced chemical wet etching proceeds on the a-plane and semipolar GaN films until chemically stable m-plane GaN surfaces as well as c-plane GaN surfaces are exposed.