Polytypism in epitaxially grown gallium nitride

Using electron and X-ray diffraction techniques as well as high-resolution transmission electron microscopy, a rhombohedral phase with the lattice par ameters a = 0.3183 nm and c = 2.338 nm has been identified in gallium nitri de (GaN) epilayers grown on sapphire by molecular beam epitaxy. A structura l model is proposed for the rhombohedral phase which corresponds to a seque nce 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. (C) 200 0 Elsevier Science B.V. All rights reserved.