Effect of amorphous and crystalline AlN buffer layers deposited on patterned sapphire substrate on GaN film quality

In recent years, aluminum nitride (AlN) and gallium nitride (GaN) heterostructures have been attracted considerable interest, especially for light emitting diode applications. In this work, 200-nm-thick AlN buffer layers were grown on patterned sapphire substrates (PSSs) via reactive radio frequency (RF) sputtering by using a mixture of argon and nitrogen gas at different powers. As the crystal quality of the AlN buffer layer improves, the surface of the GaN film grown in top of the AlN layer can achieve higher uniformity. GaN film with a thickness of 4.5 μm were grown by metal organic chemical vapor deposition, and then characterized by using field emission scanning electron microscopy and atomic force microscopy. The differences in the growth behavior of the GaN films affected the crystallinity of the GaN epitaxial film. The crystal quality of the films was evaluated by high-resolution X-ray diffraction and panchromatic cathodoluminescence, while the dislocation densities were calculated by using the full width half maximum. In this study, we investigated how the crystallinity of the AlN layer, deposited on PSS, can affect the GaN film growth and be exploited to produce high-quality GaN epitaxial layers.