Transmission electron microscope observation was performed to analyze microstructures in a (11•0)-plane GaN thin films grown by metal-organic vapour-phase epitaxy (MOVPE) on a r (1¯1•2)-plane sapphire substrate Special attention was paid to an influence of small off-angle of the substrate plane to morphology of defects in the thin films. From the transmission electron microscopic observations, the following results were drawn. (1) The crystallographic orientation relationship between GaN and sapphire substrate was:

(11•0)[00•1][¯11•0]GaN||(1¯102)[¯11•1][11•0]sapphire

The direction of +c -polarity coincides with that reported previously. (2) The pits on the surface were formed on the grain boundaries of GaN. (3) The density of pits was related with the density of nucleation of GaN-islands on the substrate. The increase in density of pits with the off-angle could be explained by the increase of nucleation sites provided by atomic steps on the substrate. (4) The side-wall planes of pits and voids were considered to be closed to ±(00•1), ±(11•4), and (11•2). (5) The formation of pits and voids were attributable to the trend that such inclined planes as (11•2) and (11•4) were stable compared with +c (00•1).

Off-Angle Dependence of Void Formation and Defect Behavior in a-Plane MOVPE-GaN on r -Plane Sapphire Substrate. N.Kuwano, A.Fukushima, Y.Kugiyama, T.Ezaki, M.Minami, M.Araki, K.Hoshino, K.Tadatomo: Physica Status Solidi C, 2009, 6[S2], S494-7