Double-crystal x-ray topography of freestanding HVPE grown n-type GaN

High-resolution X-ray topography (HRXT) and rocking curve measurements were performed on unintentionally doped, freestanding HVPE grown n-type Gallium Nitride (GaN). Based on the rocking curve widths, the dislocation density is estimated to be in the range of 10(5)-10(7)/cm(2), and the lower limit of average crystallite sizes to be 340-500 nm normal to the surface of the film. The lateral dimensions of crystallites and cavities were obtained from HRXT images, and are estimated to be in 200-500 nm, and 0.5-400 mu m ranges, respectively. Although the GaN films are freestanding, they are warped with a radius of curvature of about 0.5 m, as determined from topographic measurements. The warpage is attributed to thermal mismatch between GaN and the substrate during growth. (C) 2007 Elsevier B.V. All rights reserved.