Formation of planar defects during the initial growth of M-plane GaN on LiAlO$_{2}$(100)

We have investigated by transmission electron microscopy the structure and morphology of hexagonal GaN on tetragonal LiAlO$_{2}$ (100) during the initial stages of growth. Nucleation layers are grown by molecular beam epitaxy. The ex-situ study of the three-dimensional GaN nucleation and island coalescence reveals that planar defects, which are developed in any M-plane GaN film, are the result of the specific substrate surface morphology, and are thus growth-induced and not caused by strain relief due to the lattice mismatch