Growth of non-polar and semi-polar GaN on sapphire substrates by magnetron sputter epitaxy

Non-polar and semi-polar III-nitrides have beneficial properties for various electronic applications such as light emitting diodes and photodetectors due to the elimination or reduction of polarization effects. However, cost-effective manufacturing of non-polar and semi-polar III-nitride films with sufficient film quality is not feasible yet. We report an investigation of the morphological and structural properties of GaN grown on m-plane and r-plane sapphire by low-temperature reactive magnetron sputter epitaxy. X-ray and electron diffraction techniques are used to analyze the crystallographic orientation of the epilayer relative to the substrate, uncovering epitaxial growth of semi-polar and non-polar GaN films with single-crystal character. Although the GaN film exhibits a small tilt with respect to the substrate surface, no rotation domains are observed. Non-polar {11$\overline{2}$0} GaN grown on r-plane sapphire exhibits enhanced structural quality using lower growth temperatures, while semi-polar {11$\overline{2}$2} GaN grown on m-plane sapphire exhibits higher crystal quality when grown at higher growth temperatures. The films show structural anisotropy with the ω-FWHM of the reflection along the surface normal strongly depending on the azimuth angle with respect to the scattering plane.