OBSERVATION OF CORELESS DISLOCATIONS IN ALPHA-GAN

Large-angle convergent beam electron diffraction is used to show that hollow tubes, 5-25 nm in diameter, observed in alpha-GaN grown on sapp hire by metalorganic chemical vapor deposition, contain screw dislocat ions with Burgers vectors c (0.52 nm). It is shown that these coreless dislocations are not in an equilibrium state but may arise by the tra pping of dislocations at pinholes at an early stage of GaN growth. Alt hough pinholes may contain a, c and c + a dislocations, it is argued t hat only those containing c dislocations can survive to generate nanop ipes of constant cross-section along the [0001] axis, as observed expe rimentally.