ROLE OF THREADING DISLOCATION-STRUCTURE ON THE X-RAY-DIFFRACTION PEAKWIDTHS IN EPITAXIAL GAN FILMS

In this letter we demonstrate that the anomalously low (002) x-ray roc king curve widths for epitaxial hexagonal GaN films on (001) sapphire are a result of a specific threading dislocation (TD) geometry. Epitax ial GaN films were grown on c-plane sapphire by atmospheric pressure m etalorganic chemical vapor deposition (MOCVD) in a horizontal flow rea ctor. Films were grown with (002) rocking curves (omega-scans) widths as low as 40 arcsec and threading dislocation densities of similar to 2 x 10(10) cm(-2). The threading dislocations in this film lie paralle l to the [001] direction and within the limit of imaging statistics, a ll are pure edge with Burgers vectors parallel to the film/substrate i nterface. These TDs will not distort the (002) planes. However, distor tion of asymmetric planes, such as (102), is predicted and confirmed i n (102) rocking curve widths of 740 arcsec. These results are compared with films with (002) rocking curves of similar to 270 arcsec and thr eading dislocation densities of similar to 7 X 10(8) cm(-2). (C) 1996 American Institute of Physics.