Growth and characterization of AlGaN∕GaN heterostructures on semi-insulating GaN epilayers by molecular beam epitaxy

Al 0.30 Ga 0.70 N ∕ Ga N heterostructures grown on sapphire substrates by rf-plasma-assisted molecular beam epitaxy are investigated. The heterostructures consist of a 20nm Al0.30Ga0.70N barrier layer deposited on a 2μm semi-insulating GaN epilayer. Room-temperature mobilities averaging 1350cm2∕Vs and a sheet charge density of 1.1×1013cm−2 are consistently achieved. Central to our approach is the iron-doped semi-insulating GaN epilayer and a pulsed N∕Ga atomic deposition technique which makes it possible to simultaneously reduce threading dislocations and achieve a smooth surface. The heterostructures were examined by x-ray diffraction, transmission electron microscopy, and atomic force microscopy. Structural characterizations reveal a smooth surface morphology, coherent and sharp interfaces, and a low density of the threading dislocations.