Improvement of crystal quality of rf-plasma-assisted molecular beam epitaxy grown Ga-polarity GaN by high-temperature grown AlN multiple intermediatelayers

The effects of high-temperature-gl-own AIN multiple intermediate layers (HT -AN-MILs) on the crystal quality of Ga-polarity GaN layers grown on (0001) Al2O3 substrates by molecular beam epitaxy using rf-plasma nitrogen source were investigated. The high-temperature-grown AIN intermediate layers (HT-A IN-ILs) with different thicknesses were found to play different roles in th e improvement of crystal quality. The 8-nm-thick HT-AIN-ILs brought about i mprovement or electrical properties. On the other hand, the 2-nm-thick HT-A IN-ILs improved the surface morphology. The combination of these 8-nm-HT-AI N-ILs and 2-nm-HT-AIN-ILs improved both the electrical properties and the s urface morphology concurrently.