Improvement of electrical property and surface morphology of GaN grown by RF-plasma assisted molecular beam epitaxy by introduction of multiple AlN intermediate layer

The crystal properties of Ga-polarity GaN layers grown by molecular beam epitaxy using RF-plasma nitrogen on (0001) Al2O3 substrates were remarkably improved by introduction of high-temperature grown AlN multiple intermediate layers (HT–AlN–MILs). The effects of HT–AlN–MIL on the improvement of crystal quality were found to be different for its thickness. The 8 nm-thick HT–AlN–MIL improved the electrical property and the 2 nm-thick HT–AlN–MIL improved the surface morphology. The combination of 8 nm- and 2 nm-thick HT–AlN–MILs brought about improvement of both electrical property and surface morphology, concurrently. The HT–AlN–MIL was used for RF-MBE re-growth on MOCVD–GaN template. Relatively fine step flow structure without spiral hillocks was obtained.