Exciton-hole collision in staggered type-IIAl0.34Ga0.66

We report the phase relaxation of Γ-Γ direct excitons in staggered type-II Al0.34Ga0.66As/AlAs multiple quantum wells by means of the time-resolved degenerate four-wave mixing. The dephasing rate increases with the increase in the excitation density. Its excitation density dependence sharply changes at a critical density of 0.2 μJ/cm2. The dependence agrees with the excitation density dependence of the long-lived Γ-hole density studied by means of the pump-and-probe experiment. The long-lived hole density saturates at the same excitation density of 0.2 μJ/cm2. These facts definitely indicate that the phase relaxation rate of Γ-Γ excitons is dominated by the collision between the excitons and long-lived holes