  Two-photon time-resolved photoluminescence has been recently applied to
various semiconductor devices to determine carrier lifetime and surface
recombination velocities. So far the theoretical modeling activity has been
mainly limited to the commonly used one-photon counterpart of the technique.
Here we provide the analytical solution to a 3D diffusion equation that
describes two-photon microscopy in the low-injection regime. We focus on a
system with a single buried interface with enhanced recombination, and analyze
how transport, bulk and surface recombinations influence photoluminescence
decays. We find that bulk measurements are dominated by diffusion at short
times and by bulk recombination at long times. Surface recombination modifies
bulk signals when the optical spot is less than a diffusion length away from
the probed interface. In addition, the resolution is increased as the spot size
is reduced, which however makes the signal more sensitive to diffusion.
