CHARACTERIZATION OF DISLOCATIONS, NANOPIPES AND INVERSION DOMAINS IN GAN BY TRANSMISSION ELECTRON-MICROSCOPY

Transmission electron microscopy is used to analyse a range of defects observed in hexagonal GaN films grown on sapphire and GaN substrates by metalorganic chemical vapour deposition. Large angle convergent bea m electron diffraction is used to analyse the Burgers vectors of dislo cations and to show that hollow tubes, or nanopipes, are associated wi th screw dislocations having vectors +/- c. Weak-beam electron microsc opy shows that dislocations are dissociated into partials in the (0001 ) basal plane, but that threading segments are generally undissociated . The presence of high densities of inversion domains in GaN/sapphire films is confirmed using convergent beam electron diffraction and the atomic structure of the {10 (1) over bar 0} inversion domain boundary is determined by an analysis of displacement fringes seen in inclined domains. (C) 1997 Elsevier Science S.A.