Single heterostructures were grown onto sapphire (00•1) substrates by means of plasma-assisted molecular beam epitaxy. It was found that multi-AlN buffer layers were effective in improving the 2-dimensional electron gas mobility. A high mobility, of about 1200cm2/Vs at room temperature, was obtained by inserting 4 periods of AlN buffer layers. It was proposed that the improvement resulted from the reduction, of dislocation numbers in the films, by the multi-AlN buffer layers. When 6 periods of AlN buffer layers were used, cracks were generated at the surface.

Growth and Characterization of AlGaN/GaN Heterostructures Using Multi-AlN Buffer Layers in Plasma-Assisted Molecular Beam Epitaxy. X.Q.Shen, T.Ide, S.H.Cho, M.Shimizu, H.Okumura, S.Sonoda, S.Shimizu: Journal of Crystal Growth, 2001, 227-228, 447-52