Nonlinear optical properties of type-II quantum wells

Experimental and theoretical investigations of the near-band-gap optical nonlinearities in type-II GaAs/AlAs quantum wells are reported. The temporal evolution of the optical nonlinearities of different samples grown at our two different laboratories is analyzed by comparing femtosecond results at different pump-probe time delays with nanosecond measurements at different sample temperatures. The quasi-cw measurements at low temperatures show exciton bleaching and a pronounced heavy-hole exciton blueshift, which is absent at elevated plasma temperatures (100 K). Femtosecond spectra show a delayed onset of the exciton blueshift consistent with hole-plasma cooling in the absence of electrons. The results are analyzed using many-body theory assuming complete electron-hole charge separation. We show that the presence of a one-component plasma modifies the nonlinear optical behavior of the GaAs layer and results in dramatically different properties compared to type-I quantum-well structures.