Optimization of low temperature GaN buffer layers for halide vapor phase epitaxy growth of bulk GaN

We have studied growth and self-separation of bulk GaN on c-oriented Al2O3 using low temperature (LT) GaN buffer layers. By studying the X-ray diffraction (XRD) signature for the asymmetric and symmetric reflections versus the LT-GaN thickness and V/III precursor ratio, we observe that the peak width of the reflections is minimized using a LT buffer thickness of ~100 -300 nm. It was observed that the V/III precursor ratio has a strong influence on the morphology. In order to obtain a smooth morphology, the V/III precursor ratio has to be more than 17 during the growth of the buffer layer. By using an optimized LT buffer layer for growth of a 20 μm thick GaN layer, we obtain a XRD peak with a full width at half maximum of ~400 and ~250 arcsec for (002) and (105) reflection planes, respectively, and with a dark pit density of ~2.2 10 8 cm -2 . For layers thicker than 1 mm, the GaN was spontaneously separated and by utilizing this process, thick free freestanding 2’’ GaN substrates were manufactured.