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 organometallic vapor phase epitaxy. Transmission electron microscopy investigation shows that the nanopipes are oriented along the [0001] growth direction, and exhibit a funnel-like shape with its wider crater ended at the GaN crystal free surface. Both the crater and the pipe are generally 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 between the pipes in alpha-GaN and the micropipes (a few micrometers in diameter) observed in alpha-SiC crystals suggests that these hollow pipes are probably nucleated under the same mechanism.