Subpicosecond real-space charge transfer in GaAs/AlAs type II superlattices
The authors report time-resolved anti-Stokes Raman scattering measurements of short-period GaAs/AlAs type II superlattices which reveal directly that q approximately 0 confined and interface optical phonons are emitted by electrons when they transfer from the Gamma valley in the GaAs layers to the Xz valley in the AlAs layers in structures where the Gamma -Xz separation is greater than the optical phonon energy. The transfer time is estimated from the risetime of the non-equilibrium phonon population to be approximately=1 ps.