OPTICALLY INDUCED CARRIER TRANSFER IN SILICON ANTI-MODULATION-DOPED GAAS/ALXGA1-XAS SINGLE QUANTUM-WELLS

A series of single-quantum-well samples doped with Si in the well (antimodulation), has been investigated using photoluminescence and photoluminescence excitation spectroscopy. The photoluminescence spectra are found to show a strong dependence on the excitation photon energy, in particular as it is increased above the AlxGa1-xAs band gap. This effect is interpreted in terms of transfer to the well of free carriers photogenerated in the barrier material. The band bending in the system implies that only photoexcited electrons are transferred into the well; the resulting charge separation creates an internal field that strongly alters the confining potential of the quantum well. A dual-excitation technique allows us to control independently the potential, and probe the resulting electronic structure of the quantum well. Measurements made with picosecond-time-resolved spectroscopy also highlight the importance of free-exciton capture at impurities in the presence of an electric field. A model for the carrier-transfer process that accounts for the excitation energy threshold at the AlxGa1-xAs band gap is discussed.