High Quality A-Plane GaN Films Grown on Cone-Shaped Patterned R-Plane Sapphire Substrates

Planar nonpolar (11 (2) over bar0) 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 2 theta-omega 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 (11 (2) over bar0) GaN along [0001](GaN) and [1 (1) over bar 00](GAN) were found to be 684 and 828", respectively. As compared to the film grown on conventional r-plane sapphire substrate which typically has (11 (2) over bar0) omega FWHM values of 900 and 2124" along [0001](GaN) and [1 (1) over bar 00](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 similar to 1.0 x 10(10) cm(-2) above the flat sapphire regions to similar to 1.0 x 10(7) 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-costperformance nonpolar GaN based devices. (C) 2010 Elsevier B.V. All rights reserved.