OBSERVATION OF NANOPIPES IN ALPHA-GAN CRYSTALS

Long hollow pipes, a few nanometers in radius, have been observed for the first time in alpha-GaN films grown on sapphire substrates by orga nometallic vapor phase epitaxy. Transmission electron microscopy inves tigation shows that the nanopipes are oriented along the [0001] growth direction, and exhibit a funnel-like shape with its wider crater ende d at the GaN crystal free surface. Both the crater and the pipe are ge nerally hexagonal, although in some cases, the pipe is almost circular . These nanopipes are most likely the open-cores of screw dislocations formed under local thermodynamic equilibrium. The close similarity be tween the pipes in alpha-GaN and the micropipes (a few micrometers in diameter) observed in alpha-SiC crystals suggests that these hollow pi pes are probably nucleated under the same mechanism.