Influence of Al Preflow Time on Surface Morphology and Quality of AlN and GaN on Si(111) Grown by MOCVD

We investigate the influence of Al preflow time on surface morphology and quality of AIN and GaN. The AIN and GaN layers are grown on a Si(111) substrate by metal organic chemical vapor deposition. Scanning electron microscopy, atomic force microscopy, x-ray diffraction and optical microscopy are used for analysis. Consequently,we find significant differences in the epitaxial properties of AIN buffer and the GaN layer, which are dependent on the Al preflow time. Al preflow layers act as nucleation sites in the case of AIN growth. Compact and uniform AIN nucleation sites are observed with optimizing Al preflow at an early nucleation stage, which will lead to a smooth AIN surface. Trenches and AIN grain clusters appear on the AIN surface while melt-back etching occurs on the GaN surface with excessive Al preflow. The GaN quality variation keeps a similar trend with the AIN quality, which is influenced by Al preflow. With an optimized duration of Al preflow, crystal quality and surface morphology of AIN and GaN could be improved.