Semipolar (202̄1) GaN and InGaN quantum wells on sapphire substrates

Here, we demonstrate a process to produce planar semipolar (20 2̄1) GaN templates on sapphire substrates. We obtain (20 2̄1) oriented GaN by inclined c-plane sidewall growth from etched sapphire, resulting in single crystal material with on-axis x-ray diffraction linewidth below 200 arc sec. The surface, composed of (10 1̄1) and (10 1̄0) facets, is planarized by the chemical-mechanical polishing of full 2 in. wafers, with a final surface root mean square roughness of <0.5 nm. We then analyze facet formation and roughening mechanisms on the (20 2̄1) surface and establish a growth condition in N₂ carrier gas to maintain a planar surface for further device layer growth. Finally, the capability of these semipolar (20 2̄1) GaN templates to produce high quality device structures is verified by the growth and characterization of InGaN/GaN multiple quantum well structures. It is expected that the methods shown here can enable the benefits of using semipolar orientations in a scalable and practical process and can be readily extended to achieve devices on surfaces using any orientation of semipolar GaN on sapphire.