HVPE/MOMBE hybrid growth of high quality hexagonal GaN on SiO2 substrates with an AlN buffer layer

We tried to grow high quality GaN on a qurartz (amorphous SiO2) substrate by combining Halide VPE, which can be used to grow a thick layer at over 1000 degreesC, with MOMBE, which can be used to grow an AIN buffer layer. The MOMBE AIN buffer layer bad perfect c-axis orientation to the quartz substrate, and the GaN grown on it showed perfect c-axis orientation, too. About 20 mum thick HVPE GaN grown with an AIN buffer layer was a continuous layer whereas that grown without an AIN buffer layer was rough and had many hexagonal columns with different heights and tilted directions. In PL measurements, GaN grown with an AIN buffer layer shows clearly an excitonic emission at 358nm (3.46eV), and the e-A or D-A emission at 379nm (3.27eV) and its LO phonon replicas, whereas that without an AIN buffer layer showed only broad band edge emission.