Polytypism in epitaxially grown gallium nitride

Abstract Using electron and X-ray diffraction techniques as well as high-resolution transmission electron microscopy, a rhombohedral phase with the lattice parameters a =0.3183 nm and c =2.338 nm has been identified in gallium nitride (GaN) epilayers grown on sapphire by molecular beam epitaxy. A structural model is proposed for the rhombohedral phase which corresponds to a sequence of nine close-packed Ga–N bilayers stacked along the c -direction. Thus, the new phase can be interpreted as a long period 9R-GaN polytype.