Confinement of laser-generated carriers in semiconductors by induced lattice temperature gradients

The generation of large carrier densities in semiconductors by pulsed laser excitation can be accompanied by a large lattice temperature gradient near the surface. We formulate the coupled transport equations which describe the evolution in space and time of the carrier density and the carrier/lattice temperature below the melting point. A large temperature gradient is seen to influence the diffusion of carriers through the thermoelectric effect (which enhances diffusion) and energy band-gap gradients (which in most materials counteract diffusion). For high laser intensities we conclude that the latter effect dominates, leading to a region of carrier confinement and enhanced lattice heating near the surface.