High quality a-plane GaN films grown on cone-shaped patterned r-plane sapphire substrates

Planar nonpolar (112̅0) a-plane GaN films have been grown by metalorganic chemical-vapor deposition directly on cone-shaped patterned r-plane sapphire substrates (PRSS) fabricated by dry etching. High-resolution X-ray diffractometers 2θ-ω scan confirmed that the films grown on PRSS are solely a-plane oriented, and the full width at half maximum values (FWHM) of the X-ray rocking curves for (112̅0) GaN along [0001]GaN and [11̅00]GaN were found to be 684 and 828″, respectively. As compared to the film grown on conventional r-plane sapphire substrate which typically has (112̅0) omega FWHM values of 900 and 2124″ along [0001]GaN and [11̅00]GaN respectively, the film grown on PRSS exhibits overall reduced omega FWHM values, and much smaller anisotropy behavior of crystallinity with respect to the in-plane orientation. The surface morphology is also improved by utilizing the PRSS technique. Cross-sectional transmission electron microscopy analysis shows that the density of threading dislocations has been greatly reduced from ~ 1.0 × 1010 cm− 2 above the flat sapphire regions to ~ 1.0 × 107 cm− 2 above the protruding cone patterns. The improvement of crystal quality and the increase of light extraction efficiency by using cone-shaped PRSS technique lead to a strong enhancement in the light emission of a-plane GaN films. These results indicate that growth of a-plane GaN films on cone-shaped PRSS shows promise for use in high-quality and high-cost-performance nonpolar GaN based devices.