Reduction of the threading dislocation density in GaN films grown on vicinal sapphire (0001) substrates

Abstract

Structural properties of GaN films grown on vicinal sapphire (0001) substrates with various vicinal angles by plasma-assisted molecular beam epitaxy are investigated. High-resolution x-ray diffraction (HRXRD) results reveal the dramatic improvement of both tilting and twisting grain features of the GaN films when the vicinal angle is 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 HRXRD results. Cross-sectional transmission electron microscopy observations clearly show 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 is proposed.