Abstract
By using an improved method of two-wavelength excited photoluminescence, we observed a considerable decrease in the band-to-band photoluminescence intensity of an undoped GaAs/AlGaAs quantum well structure when a below-gap excitation was superposed on an above-gap excitation. This intensity quenching was attributed to the enhanced nonradiative recombination through below-gap states which were activated by the below-gap excitation. By changing the energy of above-gap excitation, it was shown that these below-gap states were formed neither inside GaAs well layers nor at the GaAs/AlGaAs heterointerface, but inside AlGaAs barrier layers. Tuning the photon energy of below-gap excitation revealed that the activation energy of the nonradiative recombination process via these below-gap states is around 1.2 eV. Lowering the above-gap excitation density to a single-photon-counting region enabled us to characterize below-gap states spectroscopically without the need of a high-power tunable laser source for the below-gap excitation.
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