InAs self-assembled quantum wire structures have been grown on InP substrates and studied by means of photoluminescence and polarized-light absorption measurements. According to our calculations, the observed optical transitions in each sample are consistent with wires of different heights, namely from 6 to 13 monolayers. The nonradiative mechanism limiting the emission intensity at room temperature is related to thermal escape of carriers out of the wires.
The oscillating piezoelectric field of a surface acoustic wave (SAW) is employed to transport photoexcited carriers, as well as to spatially control exciton recombination in GaAs-based nanowires (NWs) on a subns time scale. The experiments are carried out in core-shell NWs transferred to a SAW delay line on a LiNbO(3) crystal. Carriers generated in the NW by a focused laser spot are acoustically transferred to a second location, leading to the remote emission of subns light pulses synchronized with the SAW phase. The dynamics of the carrier transport, investigated using spatially and time-resolved photoluminescence, is well-reproduced by computer simulations. The high-frequency contactless manipulation of carriers by SAWs opens new perspectives for applications of NWs in opto-electronic devices operating at gigahertz frequencies. The potential of this approach is demonstrated by the realization of a high-frequency source of antibunched photons based on the acoustic transport of electrons and holes in (In,Ga)As NWs.
A theoretical model for second-order resonant Raman scattering is presented. The effect of Coulomb interaction between electrons and holes is fully taken into account in the framework of the efFective-mass approximation.By introducing discrete and continuous excitonic intermediate states in the Raman process, an explicit expression for the Raman scattering eKciency is given for long-range Frohlich electron-phonon interaction. The model developed can be used to evaluate Raman profiles around the resonant region. A closed-form expression for all matrix elements of the exciton-phonon interaction is obtained once the Coulomb problem for the relative electronhole motion is separated in spherical coordinates. For the first time, to our knowledge, transitions between states from the excitonic ionization continuum for nonzero phonon wave vectors are exactly included in the calculations. The dependence of the Raman scattering efBciency on electron and hole masses is analyzed. The contribution of the different excitonic transitions to the scattering process is also studied. Finally, the model is compared to available experimental data for GaP, InP, GaAs, and GaSb. The overall agreement with the measured resonance profiles and their absolute scattering efBciencies confirms that excitonic effects are required for a satisfactory interpretation of these phenomena.
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