Highly-crystalline 6 inch free-standing GaN observed using X-ray diffraction topography

Abstract

We demonstrate the crystal quality of a 6 inch (0001) plane free-standing GaN substrate grown using a Na-flux based liquid phase epitaxy method. The 114 rocking curve profiles of every point over the substrate were recorded by synchrotron X-ray diffraction topography. The reconstructed images show that there is a huge boundary between the high crystalline area and the low crystalline area in the substrate. Anisotropic bowing of the lattice planes with respect to the [100] direction was obtained from wafer bending analysis. The mean width of the rocking curves over the wafer was 0.024°, which indicates that the newly fabricated 6 inch GaN substrate was almost a single crystal. We found that there was a competition between crystallinity and homogeneity.