Trapping Mechanism to Account for Persistent Photoeffects in Heavily, Doped GaAs/AlGaAs Multiple Quantum Wells
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We have investigated trapping mechanisms responsible for the persistent photoeffect in heavily doped GaAs/Al0.3Ga0.7As multiple-quantum-well structures. The study was performed using infrared-absorption techniques to study the intersubband transitions of the wells as a function of secondary illumination. The frequency of the secondary illumination was varied by the use of filters on the secondary source. The peak energies of the intersubband transitions can be modeled using the nonparabolic anisotropic envelope-function approximation, which accounts for many-body effects due to the high doping level. The red shift in the intersubband transition energy observed on secondary illumination indicates a decrease in the carrier concentration in the wells due to trapping in the barrier. We have found a decrease in the strength of the persistent photoeffect when the energy of the photons used in the secondary illumination is below the band gap of Si (1.172 eV) This observation is consistent with optically activated traps whose activation energy is ≥ 1.172 eV. These data, along with temperature recovery data, make the most probable candidate for the trap the DX center.