Dynamics of exciton formation and relaxation in GaAs quantum wells

Abstract

We show that excitons form with a time constant \ensuremath{\tau}\ensuremath{\le}20 ps following the creation of electron-hole pairs by subpicosecond optical excitation. The excitons are initially formed in large-wave-vector states. At low temperatures, these nonthermal excitons relax in \ensuremath{\approxeq}400 ps to the K\ensuremath{\approxeq}0 states, which couple directly to light by interaction with other excitons and acoustic phonons. This leads to a slow rise of exciton luminescence and an unusual dependence of this rise time on temperature, excitation density, and excitation energy.