Reduction of hexagonal defects in N-polar AlGaN epitaxial layers grown with reformed pulsed-flow technology

Abstract

The N-polar AlGaN epi-layers were successfully grown on (0001) c-plane sapphire substrates by using the reformed metal-organic chemical vapor deposition technology featured with an optimized pulsed NH3-flow supplying scheme. In order to reduce the hexagonal defects in the N-polar AlGaN epi-layers, the conventional NH3 pulsed-flow technology was reformed. Particular attention should be paid on the impacts of the variation in the duty ratio and the NH3-purge term within each growth cycle on the surface morphology and crystalline quality of the grown N-polar AlGaN epi-layers. A smooth surface morphology with a root-mean-square value as small as 5.7 nm was obtained. On the other hand, the significantly decreased density of the hexagonal defects confirmed with microscope and X-ray diffraction measurements implies a remarkable improvement in crystalline quality of the N-polar AlGaN epi-layers. These results indicate that the reformed pulsed-flow technology with an optimized source supplying scheme plays a crucial role in improving the surface morphology and crystalline quality of the N-polar AlGaN epi-layers.