Nonlinear optical dynamics of excitons and trions

We investigate the nonlinear optical dynamics of excitons and trions in CdTe modulation‐doped quantum wells by time and spectrally resolved pump–probe experiments. We find that the nonlinearities induced by excitons are different from those due to the presence of the trions. From a comparison between the exciton and trion behaviours, we show that, at low temperature, trions are formed from excitons in about 10 picoseconds and, as the temperature is increased, a thermal equilibrium is reached between exciton and trion populations within 5 picoseconds.