We reported 2~4-inch bulk GaN growth by Hydride Vapor Phase Epitaxy (HVPE). Sapphire substrate was used as the starting substrate. An optical reflectance system was assembled in the HVPE system, which can detect the in-situ reflectivity and the stress of the epilayer simultaneously. By fabricating different nano-structure on the surface of the starting substrate, strain distribution can be modulated in the following thick GaN layer grown by HVPE. Fluid dynamics and growth kinetics were theoretically simulated, the stress and dislocation evolution in HVPE growth of GaN was characterized by confocal micro-Raman spectroscopy, high resolution XRD, cathodoluminescence, TEM, and in-situ optical monitoring, providing unambiguous understandings in critical issues of GaN substrate fabrication by HVPE.
The FWHMs of x-ray rocking curve of GaN (002) and (102) reflection were both about 30~40arcsec, dislocation etching pits density is in 104cm-2 order. The un-doped bulk GaN has background electron concentration in the order of 1016cm-3, and electron mobility of around 1400V·s/cm2.
In the presentation, we will also review other growth methods, such as Na-flux method, ammonothermal method, for bulk GaN growth. Homoepitaxial growth of GaN was also discussed.