  Herein we review the remarkable range of modifications to materials
properties associated with photoexcitation of the growth surface during
physical vapor epitaxy of semiconductors. We concentrate on mechanisms
producing measureable, utilizable changes in crystalline perfection, phase,
composition, doping, and defect distribution. We outline the relevant physics
of different mechanisms, concentrating on those yielding effects orthogonal to
the primary growth variables of temperature and atomic or molecular fluxes and
document the phenomenological effects reported. Based on experimental
observations from a range of semiconductor systems and growth conditions, the
primary effects include enhanced anion desorption, molecular dissociation,
increased doping efficiency, modification to defect populations and
improvements to the crystalline quality of epilayers grown at low temperatures.
Future research directions and technological applications are also discussed.
