Trion dephasing by electron scattering in GaAs/AlAs quantum wells

We report on the photoluminescence in quantum wells that have a low-density (n_e < 2 × 10¹⁰ cm^-2) two-dimensional electron gas (2DEG). Mixed type I-type II GaAs/AlAs quantum wells are studied in which the 2DEG is photogenerated in the type I quantum wells and n_e is determined by the excitation intensity. The photoluminescence spectrum at T = 2 K is dominated by the recombination of a complex consisting of an electron bound to an exciton (a trion). It has a Lorentzian line shape whose width increases with increasing n_e. This dependence is attributed to trion-electron scattering processes. We present a model of the elastic trion-electron scattering and calculate its rate as a function of n_e. The model is based on a pair Coulomb interaction, and we fit the trion linewidth dependence on n_e by using the 2DEG screening wave vector (q_s) as a free parameter. The intensity at the low-energy tail of the trion band increases with n_e, and we attribute it to inelastic trion-electron scattering processes.