Selective area epitaxy at the nanoscale enables fabrication
of
high-quality nanostructures in regular arrays with predefined geometry.
Here, we investigate the growth mechanisms of GaAs nanoridges on GaAs
(100) substrates in selective area trenches by metal–organic
vapor-phase epitaxy (MOVPE). It is found that pre-growth annealing
results in the formation of valley-like structures of GaAs with atomic
terraces inside the trenches. MOVPE growth of GaAs nanoridges consists
of three distinct stages. Filling the trench in the first stage exhibits
a step-flow growth behavior. Once the structure grows above the mask
surface, it enters the second stage of growth by forming {101} side
facets as the (100) flat top facet progressively shrinks. In the third
stage, the fully formed nanoridge begins to overgrow onto the mask
with a significantly reduced growth rate. We develop a kinetic model
that accurately describes the width-dependent evolution of the nanoridge
morphology through all three stages. MOVPE growth of fully formed
nanoridges takes only about 1 min, which is 60 times faster than in
our set of molecular beam epitaxy (MBE) experiments reported recently,
and with a more regular, triangular cross-sectional geometry defined
solely by the {101} facets. In contrast to MBE, no material loss due
to Ga adatom diffusion onto the mask surface is observed in MOVPE
until the third stage of growth. These results are useful for the
fabrication of GaAs nanoridges of different dimensions on the same
substrate for various applications and can be extended to other material
systems.