GaN single crystals were used as substrates
for MOCVD growth. The (0 0 0 (1) over bar) plane of the substrate crystals
was polished to obtain off-angle orientations of 0, 2, and 4 degrees towards
the [1 0 (1) over bar 0] direction. The highest misorientation resulted
in a reduction of the hexagonal hillock density by nearly two orders of
magnitude as compared with homo-epitaxial films grown on the exact (0 0
0 (1) over bar) surface. The features that are still found on the 4 degrees
off-angle sample after growth can be explained by a model involving the
interaction of steps, introduced by the misorientation, and the hexagonal
hillocks during the growth process. Following from this explanation it
could be concluded that surface diffusion is found to be not important
during growth on the N-side. The material quality of the N-side was examined
by photoluminescence (PL) measurements. The PL spectrum measured at 5 K
shows dominant donor bound excitons with a FWHM of 1.4 meV as well as free
excitonic transitions. (C) 2000 Elsevier Science B.V. All rights reserved.