No abstract

No abstract

Picosecond lasers allow to detect the dynamics of excitons directly in the time domain. Here examples of such experiments are presented for high quality AlGaAs MQW samples at low temperatures and in the low and medium density regime. The phase relaxation time T2 is measured in FWM experiments and quantum beats are observed between the hh and lh exciton and between exciton and biexciton states. A value of the biexciton binding energy of 1.75 meV is deduced in agreement with our luminescence data. The T2 times are compared with scattering times z obtained from diffusion measurements using ps and ns laser-induced gratings. Interface-roughness scattering occurs only for thermalized excitons. The influence of increasing exciton-exciton scattering with density is demonstrated for (magneto-) excitons and Landau levels. Finally the luminescence dynamics of excitons is investigated for resonant and nonresonant excitation. The influence of cooling (intraband relaxation) is discussed and a simple model is presented to explain the generally observed increase of the lifetime TI with lattice temperature.

No abstract

No abstract