Resonant Γ-X-transfer in GaAs/AlAs quantum-well structures

We investigate the Γ2-Xz1 intersubband dynamics in GaAs/AlAs quantum-well structures by time-resolved infrared pump and probe experiments. In the studied structure, the second Γ level in GaAs is nearly resonant to the first Xz level in AlAs. We observe bi-exponentially decaying signals with a short time constant of the order of 1 ps and a longer time constant of about 7 ps at 10 K and 4 ps at 300 K respectively. The long-term decay represents the Xz-Γ2 transfer by elastic Γ-X scattering at low temperatures. At 300 K electron-LO phonon scattering accelerates the Γ-X transfer.