Γ-X electron transfer in type II tunneling bi-quantum wells

We have studied the energy band structure and the Γ-X carrier transfer mechanism for type II tunneling bi-quantum wells consisting of GaAs wells, AlGaAs barriers of different thicknesses, and AlAs layers by cw and time-resolved photoluminescence measurements. The cw photoluminescence spectra of the indirect recombination of X electrons in the 7.1 nm thick AlAs layers with Γ holes in the 2.8 nm thick GaAs wells show weak zero-phonon lines indicating that the AlAs confined states at X_xy are lower than those at Y_z. Time-resolved photoluminescence reveals that the carrier transfer time depends stronger on temperature for thicker AlGaAs barriers. Two scattering mechanisms, temperature-dependent phonon scattering and the temperature-independent interface scattering, are probably involved in the carrier transfer, the latter becoming smaller with increasing AlGaAs barrier thickness. Our results are compared with those obtained for similar type II GaAs/AlAs superlattices.