GAMMA-X ELECTRON-TRANSFER IN TYPE-II TUNNELING BI-QUANTUM WELLS

We have studied the energy band structure and the GAMMA-X carrier transfer mechanisms for type II tunneling bi-quantum wells consisting of GaAs wells, barriers of different thicknesses, and AlAs layers by cw and time-resolved photoluminescence measurements. The cw photoluminescence spectra of the direct recombination of X electrons in the 7.1 nm thick AlAs layers with GAMMA holes in the 2.85 nm thick GaAs wells show weak zero-phonon lines indicating that the AlAs confined states at X(xy) are lower than those X(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 smaller type II GaAs/AlAs superlattices.