Dislocation arrangement in a thick LEO GaN film on sapphire

Diffraction-contrast TEM, focused probe electron diffraction, and high-reso lution X-ray diffraction were used to characterize the dislocation arrangem ents in a 16 mum thick coalesced GaN film grown by MOVPE LEO. As is commonl y observed, the threading dislocations that are duplicated from the templat e above the window bend toward (0001). At the coalescence plane they bend b ack to lie along [0001] and thread to the surface. In addition three other sets of dislocations were observed. The first set consists of a wall of par allel dislocations lying in the coalescence plane and nearly parallel to th e substrate, with Burgers vector (b) in the (0001) plane. The second set is comprised of rectangular loops with b = 1/3 [11 (2) over bar0] (perpendicu lar to the coalescence boundary) which originate in the coalescence boundar y and extend laterally into the film on the (1 (1) over bar 00). The third set of dislocations threads laterally through the film along the [1 (1) ove r bar 00] bar axis with 1/3<11 <(2)over bar>0>-type Burgers vectors These s ets result in a dislocation density of similar to 10(9) cm(-2) High resolut ion X-ray reciprocal space maps indicate wing tilt of similar to0.5 degrees .