Structural properties of GaN buffer layers on 4H-SiC(0001) grown by plasma-assisted molecular beam epitaxy for high electron mobility transistors

The structural properties of GaN buffer layers grown on 4H-SiC(0001) by plasma-assisted molecular beam epitaxy were investigated. Films grown under intermediate and N-rich conditions exhibited lower dislocation densities and lower residual lattice mismatch strain than Ga-rich grown films. To overcome the rough surfaces associated with intermediate and N-rich growth, two-step GaN buffers were investigated where the first layer was grown in the intermediate growth regime and the second layer at the boundary to Ga droplet formation. It is demonstrated that for our growth conditions a buffer thickness of 100nm grown in intermediate conditions was necessary and sufficient for dislocation reduction. High electron mobility transistor structures grown using this Ga-flux strategy exhibit mobilities, power densities and power added efficiencies in excess of 1400 cm(2)/V(.)s, 12 W/mm and 46% at 4 GHz, respectively.