Structural properties of GaN films grown on vicinal sapphire (00▪1) substrates with various vicinal angles by plasma-assisted molecular beam epitaxy were investigated. High-resolution X-ray diffraction results revealed the dramatic improvement of both tilting and twisting grain features of the GaN films when the vicinal angle was larger than 0.5° with the formation of multilayer macro-steps on the surface. The threading dislocation density reduces by over an order of magnitude estimated from the high-resolution X-ray diffraction results. Cross-sectional transmission electron microscopy observations clearly showed that the formation and lateral propagation of macro-steps on the GaN surface play an important role in this dislocation reduction. A method for the reduction of threading dislocation density in GaN epilayers was proposed.

Reduction of the Threading Dislocation Density in GaN Films Grown on Vicinal Sapphire (0001) Substrates. X.Q.Shen, H.Matsuhata, H.Okumura: Applied Physics Letters, 2005, 86[2], 021912 (3pp)