Transmission electron microscope observations were used to analyze

microstructures in a (11•0)-plane GaN thin films grown by metal-organic vapourphase

epitaxy (MOVPE) onto 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 TEM observations, the following conclusions

were drawn. (1) The crystallographic orientation relationship between GaN and

sapphire substrate was (11•0)[00•1][¯11•0]GaN||(1¯1•2)[¯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 can 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 inclining planes

as (11•2) and (11•4) were stable compared with +c (00•1). A possible technique for

reduction of defects was also discussed.

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