Lattice distortions in GaN thin films on (0001) sapphire

The GaN/sapphire microstructure and lattice distortions in GaN were investigated using convergent beam electron diffraction (CBED) and electron backscatter diffraction (EBSD). CBED studies showed small scale (<10) triclinic strain in the electron microscope specimens with a tetragonal expansion (∼0.001 nm) of the lattice along the GaN growth direction, which has been observed in continuous films as well as isolated or partly coalesced islands. The strains extend up to ∼ 2 μm from the GaN/sapphire interface. EBSD studies show a clear mosaic structure. The largest component of the mosaic structure corresponds to a twist around the [0001] axis, perpendicular to the interface.