  We report the engineering of air-voids embedded in GaAs-based photonic
crystal surface emitting lasers realised by metalorganic vapour-phase epitaxy
regrowth. Two distinct void geometries are obtained by modifying the photonic
crystal grating profile within the reactor prior to regrowth. The mechanism of
void formation is inferred from scanning transmission electron microscopy
analysis, with the evolution of the growth front illustrated though the use of
an AlAs/GaAs superlattice structure. Competition between rapid lateral growth
of the (100) surface and slow diffusion across higher index planes is exploited
in order to increase void volume, leading to an order of magnitude reduction in
threshold current and an increase in output power through an increase in the
associated grating coupling strength.
