DYNAMICS OF EXCITONIC STATES IN GAAS ALGAAS QUANTUM-WELLS/

The influence of photoexcited carriers on the dynamics of the absorpti on spectra of GaAs/AlxGa1-xAs multilayer quantum wells is investigated experimentally. It is found that at quasiparticle densities all the w ay up to 10(11) cm(-2) the saturation of the excitonic absorption is d ue to both a decrease of oscillator strength and broadening of the exc itonic lines. It is shown that in the case of femtosecond resonance la ser excitation the decrease of oscillator strength is due to free elec tron-hole pairs, while the broadening and energy shift of the excitoni c lines are due to the exciton-exciton interaction. The lifetimes of f ree electron-hole pairs and excitons (approximate to 65 ps and approxi mate to 410 ps, respectively) are determined from the exponential decr ease of the change in the oscillator strength and in the width and ene rgy position of the excitonic lines. (C) 1997 American Institute of Ph ysics.