EXCITON DYNAMICS IN GAAS QUANTUM-WELLS

We show that excitons in GaAs quantum wells are formed in less than 20 ps following subpicosecond optical excitation. The rise of exciton luminescence is surprisingly slow ( ≈ 400 ps) in spite of the fast formation of excitons. The slow rise of exciton luminescence shows unusual dependence on temperature, density and excitation energy. We show that the slow rise of exciton luminescence is caused by the slow relaxation of excitons within the excitonic branch. These studies raise a number of fundamental issues which are discussed. © 1990.