Spontaneous emission in highly excited semiconductors: Saturation of the radiative recombination rate

The spontaneous emission rate of semiconductors displays a saturation at high carrier injection densities due to the filling of the conduction and valence bands. We have carried out time-resolved experiments, whereby a semiconductor quantum well at room temperature is excited optically by a short laser pulse and the time decay of its luminescence is measured for different injected carrier densities. The luminescence decay rate, plotted as a function of injected carrier density, deviates strongly from the well-known quadratic recombination law, valid at low carrier densities, displaying a saturation. We have developed a simple analytic theory that accounts for this saturation and can describe adequately the recombination kinetics of highly excited semiconductor quantum wells.