Impurity-induced modulation of terahertz waves in optically excited GaAs

The effect of the photoinduced absorption of terahertz (THz) radiation in a semi-insulating GaAs crystal is studied by the pulsed THz transmission spectroscopy. We found that a broad-band modulation of THz radiation may be induced by a low-power optical excitation in the spectral range of the impurity absorption band in GaAs. The measured modulation achieves 80\%. The amplitude and frequency characteristics of the resulting THz modulator are critically dependent on the carrier density and relaxation dynamics in the conduction band of GaAs. In semi-insulating GaAs crystals, the carrier density created by the impurity excitation is controlled by the rate of their relaxation to the impurity centers. The relaxation rate and, consequently, the frequency characteristics of the modulator can be optimized by an appropriate choice of the impurities and their concentrations. The modulation parameters can be also controlled by the crystal temperature and by the power and photon energy of the optical excitation. These experiments pave the way to the low-power fast optically-controlled THz modulation, imaging, and beam steering.Comment: 5 pages, 3 figure

Spin dynamics in the charged InP quantum dots

Physics of semiconductors 2002 : proceedings of the 26th International Conference on the Physics of Semiconductors held in Edinburgh UK 29 July-2 August 2002conference pape

Optical Orientation Of Electron And Nuclear Spins In Negatively Charged InP QDs

Light-induced spin orientation in negatively charged InP quantum dots is shown experimentally to be conserved for about 1 ms

Temperature behavior of hot carrier dynamics in InP quantum dots

Photoluminescence (PL) kinetics of the InP self-assembled quantum dots is studied under quasiresonant optical excitation in the temperature range 10–100 K. It is found that the PL rise time abruptly drops with increasing temperature. The model calculations based on the rate equations have shown that this drop cannot result from thermostimulated phonon relaxation of the hot carriers. We developed a model assuming that the main reason for variations in the PL kinetics is related to thermal ejection ("evaporation") of holes from the quantum dots, with a fraction of the dots acquiring negative charge. The model allowed us to describe quantitatively the PL rise as well as the PL decay over the whole temperature range under study. We identified also a number of effects caused by electron evaporation from the quantum dots at temperatures above 60 K. Comparison of the results of the model calculations with the experimental data has allowed us to determine rate parameters of the ejection processes

Fine structure and spin dynamics of excitons in the GaAs/AlxGa1-xAs superlattices

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Spin dynamics of carriers in GaAs quantum wells in an external electric field

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Fine structure and spin quantum beats in InP quantum dots in a magnetic field

The paper reports on quantum beats observed in the photoluminescence kinetics of a single layer of the InPself-assembled quantum dots in a magnetic field. It is found that the beats arise only after removal of excesscharges from the quantum dots by an external electrical bias. The quantum beats are shown to be related to theinterference of the excitonic fine-structure states split by the magnetic-field. The dependences of the beatcharacteristics on the magnetic-field strength and orientation are studied. Theoretical analysis based on a modelspin Hamiltonian has allowed us to describe adequately the shape of the oscillating component of the signal.We have determined the values of the electron g-factor components and estimated the spread and the meanvalue of the hole g factor, as well as of the electron-hole exchange splitting parameters