High-quality AlGaN/GaN grown on sapphire by gas-source molecular beam epitaxy using a thin low-temperature AlN layer

Growth of high-quality AlGaN/GaN heterostructures on sapphire by ammonia gas-source molecular beam epitaxy is reported. Incorporation of a thin AlN layer grown at low temperature within the GaN buffer is shown to result in enhanced electrical and structural characteristics for subsequently grown heterostructures. AlGaN/GaN structures exhibiting reduced background doping and enhanced Hall mobilities (2100, 10310 and 12200 cm²/Vs with carrier sheet densities of 6.1 × 10¹² cm^-2, 6.0 × 10¹² cm^-2, and 5.8 × 10¹² cm^-2 at 300 K, 77 K, and 0.3 K, respectively) correlate with dislocation filtering in the thin AlN layer. Magnetotransport measurements at 0.3 K reveal well-resolved Shubnikov-de Haas oscillations starting at 3 T.