Bleaching compensation in GaAs/AlGaAs quantum wells by above-barrier illumination

Abstract

Abstract. We report an experimental study of the nonlinear response of single GaAs/AlGaAs quantum well. It was shown that bleaching effect manifested as reversible exciton spectral lines broadening can be suppressed by additional above-barrier illumination. IntroductionOne of the most promising alternatives to current silicon-based electronics is the information processing in purely optical way [1][2][3]. Exciton and excitonic complexes in A3B5 nanostructures strongly interact with light due to the relatively large oscillator strength and could serve as a physical model of two-level system that draws special attention in the area of optical computing. However bleaching effect manifested as reversible exciton spectral line broadening limits usefulness of GaAs/AlGaAs structures in informational photonics.Earlier it was shown that at relatively weak and intermediate intensities exciton bleaching is observed while spectrally integrated peak intensity in the absorption spectrum remains the same [4]. The main mechanism of bleaching is said to be broadening of the exciton line induced by scattering of excitons on carriers and exciton-carriers complexes. Сarriers captured in QW reveal long-lived kinetics in microsecond scale [5]. Moreover PL signal from electron hole pair could be clearly detected up to tens of second after excitation due to non-exponential decay of carrier concentration [6,7]. Bleaching effect could be reduced by lowering of Al percentage in Al Ga 1− As QW barriers down to few percent [8].Carriers could be observed even in nominally undoped quantum wells (QWs) grown by Molecular Beam Epitaxy (MBE) due to the unintentional doping. Presence of carriers in QW leads to the formation of a peak in the photoluminescence (PL) spectrum at energies below exciton recombination line [9] . This peak corresponds to the exction-carrier bound state -trion. Additional optical pump could lead either to the buildup or to the reduction of charge carriers concentration in QW depending on the pump spectral position relative to the band gap [10]. Alterations in carriers concentration or even in their sign [11] may be revealed by analysis of opposing changes in trion and exciton peak amplitudes in PL.PL spectroscopy is generally used for detection of such charged exciton complexes [5,[9][10][11]. Still it could not give the full picture of the exciton dynamics due to the difficulty of the factorization of the exciton resonance width. We propose the Brewster angle reflection

Modeling and optimization of the excitonic diffraction grating

“…For QW used in [12] Γ R Γ N R ≈ 0.3. For higher quality molecular beam epitaxy grown QWs this ratio could reach 0.45 for GaAs/Al 0.3 Ga 0.7 As QWs [13], 0.6 for GaAs/Al 0.03 Ga 0.97 As QWs [14]. It also could exceed unity for thin [15] and thick [16] In x Ga 1−x As/GaAs (x < 0.1) QWs.…”