EFFECT OF FREE ELECTRON-HOLE PAIRS ON THE SATURATION OF EXCITONIC ABSORPTION IN GAAS ALGAAS QUANTUM-WELLS/

The pump-probe experimental method is used to investigate the effect o f photoexcited carriers on the dynamics of the exciton absorption spec tra of GaAs / AlxGa1-xAs-multilayer quantum wells. Use of the method o f moment analysis for processing the results makes it possible to iden tify the simultaneous contribution of changes in oscillator strength a nd width of the exciton lines in the saturation of exciton absorption. It was found that the oscillator strength recovers its initial value in the course of the first 100-130 ps, whereas broadening and energy-s hift of the exciton lines is observed for 700-800 ps. These are the fi rst experimental measurements of the excitation densities at which the oscillator strength of the excitonic state saturates when the latter is perturbed only by free-electron-hole pairs, and when it is perturbe d only by other excitons. (C) 1998 American Institute of Physics.