Basal plane misfit dislocations and stress relaxation in III-nitride semipolar heteroepitaxy

This article presents a theoretical analysis of dislocation behavior and stress relaxation in semipolar III-nitride heteroepitaxy, e.g., for AlxGa1-xN and InyGa1-yN layers grown on {hh (2) over bar(h) over barm}- or {h0 (h) over barm}-type semipolar planes of GaN substrates. We demonstrate that the shear stresses on the unique inclined basal (0001) plane do not vanish for such growth geometries. This leads to the onset of relaxation processes in semipolar III-nitride heterostructures via dislocation glide in the basal slip systems <(1) over bar(1) over bar 20 >(0001) and to the formation of misfit dislocations (MDs) with Burgers vectors of (a/3)<(1) over bar(1) over bar 20 >-type at the semipolar heterointerface. Next we calculate the Matthews-Blakeslee critical thickness for MD formation in semipolar III-nitride layers together with the MD equilibrium spacings for complete misfit relaxation. The component of the MD Burgers vector normal to the film/substrate interface will cause a crystal lattice tilt in the epilayer with respect to the GaN substrate. The calculated magnitudes of the tilt angles are 0.62 degrees and 0.67 degrees for AlxGa1-xN and InyGa1-yN alloys with compositions of x = 0.20 and y = 0.07, respectively, grown in the (11 (2) over bar2) semipolar orientation. The modeling results are discussed in light of recent experimental observations [A. Tyagi et al., Appl Phys. Lett. 95, 251905 (2009); E. Young et al., Appl. Phys. Express 3, 011004 (2010); and F. Wu etal., J. Appl. Phys. 109, 033505 (2011)] of MDs and crystal lattice tilt in semipolar III-nitride heteroepitaxial layers. (C) 2011 American Institute of Physics. [doi:10.1063/1.3590141]