Title: Island dynamics and anisotropy during vapor phase epitaxy of m-plane GaN,
Abstract: Using in situ grazing-incidence x-ray scattering, we have measured the
diffuse scattering from islands that form during layer-by-layer growth of GaN
by metal-organic vapor phase epitaxy on the (1010) m-plane surface. The diffuse
scattering is extended in the (0001) in-plane direction in reciprocal space,
indicating a strong anisotropy with islands elongated along [1 $\overline{2}$
10] and closely spaced along [0001]. This is confirmed by atomic force
microscopy of a quenched sample. Islands were characterized as a function of
growth rate G and temperature. The island spacing along [0001] observed during
the growth of the first monolayer obeys a power-law dependence on growth rate
G$^{-n}$, with an exponent $n = 0.25 \pm 0.02$. Results are in agreement with
recent kinetic Monte Carlo simulations, indicating that elongated islands
result from the dominant anisotropy in step edge energy and not from surface
diffusion anisotropy. The observed power-law exponent can be explained using a
simple steady-state model, which gives n = 1/4.