  The evolution of surface morphology during the growth of N-polar (000-1) GaN
under N-rich condition is studied by kinetic Monte Carlo (kMC) simulations for
two substrates miscuts 2deg and 4deg. The results are compared with
experimentally observed surface morphologies of (000-1) GaN layers grown by
plasma-assisted molecular beam epitaxy. The proposed kMC two-component model of
GaN(000-1) surface where both types of atoms: nitrogen and gallium attach the
surface and diffuse independently, explains that at relatively high rates of
the step flow (miscut angle <2deg) the low diffusion of gallium adatoms causes
surface instabilities and leads to experimentally observed roughening while for
low rates of the step flow (miscut 4deg), smooth surface can be obtained. In
the presence of almost immobile nitrogen atoms under N-rich conditions, the
growth is realized by the process of two-dimensional island nucleation and
coalescence. Additionally, we show that higher crystal miscut, lower crystal
growth rate or higher temperature results in similar effect of the smoothening
of the surface. We show that the surface also smoothens for the growth
conditions with very high N-excess. The presence of large number of nitrogen
atoms changes locally mobility of gallium atoms thus providing easier
coalescence of separated island.
