Lattice Tilt and Misfit Dislocations in (1122) Semipolar GaN Heteroepitaxy

Epilayer lattice tilt has been observed by X-ray diffraction for heteroepitaxial AlGaN and InGaN films on (1122) semipolar GaN substrates. Complementary transmission electron microscopy demonstrates that epilayer tilt is a consequence of interfacial misfit dislocations with Burgers vectors a /3[1120] that glide on the (0001) basal plane [inclined ∼58° to (1122)]. The dislocation lines are parallel to [1100], consistent with the anisotropy of the tilt observed in X-ray scans parallel to orthogonal in-plane directions. The dislocations had an in-plane Burgers vector component that relieved misfit strain, and a perpendicular component responsible for lattice tilt. Dislocation densities predicted by tilt agree well with TEM measurements.