The growth and transport characteristics of high-density (1013/cm2) 2-dimensional electron gases confined at AlGaN/GaN interfaces grown by plasma-assisted molecular-beam epitaxy on sapphire substrates were studied. A sequence of two Ga/N ratios was used during growth of the insulating GaN buffer layer. The 2-step buffer layer permitted simultaneous optimizations of a reduction in threading dislocations and of the surface morphology.

Dislocation and Morphology Control during Molecular-Beam Epitaxy of AlGaN/GaN Heterostructures Directly onto Sapphire Substrates. M.J.Manfra, N.G.Weimann, J.W.P.Hsu, L.N.Pfeiffer, K.W.West, S.N.G.Chu: Applied Physics Letters, 2002, 81[8], 1456-8