Important structural characteristics (correlation lengths of columnar crystallites, dislocation densities, angles of rotational disorder) were determined in the hexagonal phase, after its metal-organic chemical vapour deposition onto c-plane sapphire, by means of transmission electron microscopy and triple-axis X-ray diffractometry. The films exhibited edge dislocation densities which were of the order of 1011/cm2, tilt and twist angles of 0.1º and 1.3º, respectively, and a columnar structure with lateral and vertical correlation lengths of 150 and 1000nm. It was shown that triple-axis X-ray diffractometry was a good technique for distinguishing between defects, such as edge and screw dislocations, that led to a characteristic broadening of symmetrical and asymmetrical Bragg reflections.

T.Metzger, R.Höpler, E.Born, O.Ambacher, M.Stutzmann, R.Stömmer, M.Schuster, H.Göbel, S.Christiansen, M.Albrecht, H.P.Strunk: Philosophical Magazine A, 1998, 77[4], 1013-25