Selective area epitaxy of InGaN quantum well triangular microrings with a single type of sidewall facets

Triangular microrings have been formed by selective area epitaxy of GaN and InGaN quantum wells (QWs) on patterned (0 0 0 1) AlN/sapphire. SiO₂ patterns consist of triangular ring openings oriented with edges parallel to two different orientations. InGaN QW microrings with each edge parallel to the 〈1 1̄ 0 0〉 direction have very rough sidewalls while microrings with each edge parallel to the 〈1 1 2- 0〉 direction exhibit well formed and smooth sidewalls as a result of the generation of a single type of {1 1̄ 0 1} facets on the inner and outer sidewalls. These {1 1̄ 0 1} facets demonstrate similar cathodoluminescence (CL) spectra that appear to be the superposition of two peaks at photon energies ∼2.5 eV (500 nm) and 2.7 eV (460 nm). Moreover, spatially matched striations are observed in the CL intensity images and surface morphologies of the {1 1̄ 0 1} sidewall facets. The observed striations are found to be related to subtle surface morphologies of the underlying GaN structures.