DYNAMICS OF EXCITON FORMATION AND RELAXATION IN GAAS QUANTUM-WELLS

We show that excitons form with a time constant 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 400 ps to the K0 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. © 1990 The American Physical Society.