It was demonstrated that the anomalously low (002) X-ray rocking curve widths of epitaxial hexagonal nitride films on (001) sapphire were the result of a specific threading dislocation geometry. Epitaxial films were grown onto c-plane sapphire by means of atmospheric-pressure metalorganic chemical vapor deposition in a horizontal flow reactor. Films were grown which had (002) rocking curve widths that were as low as 40arcsec and had threading dislocation densities of about 2 x 1010/cm2. The threading dislocations in the film lay parallel to the [001] direction and were within the limits of imaging statistics. All of them were of pure edge-type, with Burgers vectors that were parallel to the film/substrate interface. Such threading dislocations did not distort the (002) planes. However, a distortion of asymmetrical planes, such as (102), was predicted and was confirmed by (102) rocking curve widths of 740arcsec. The results were compared with those for films with (002) rocking curves of about 270arcsec and threading dislocation densities of about 7 x 108/cm2.

B.Heying, X.H.Wu, S.Keller, Y.Li, D.Kapolnek, B.P.Keller, S.P.DenBaars, J.S.Speck: Applied Physics Letters, 1996, 68[5], 643-5