2. Articole

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Author: search.filters.author.Gurau, Virginia

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    Multiplasmon radiation line replicas of bound excitons in single ZnSe crystals [Articol]
    (2006) Klyukanov, Alexandr; Sushkevici, Konstantin; Chyukichev, M.; Awawdeh, Adnan; Gurau, Virginia; Catanoi, A.
    The cathode-luminescence of ZnSe single crystals, grown from vapour phase and heat treated in Bi melts [ZnSe(Bi)] at 1200 K for 120h, and also in Bi melts doped by Al [ZnSe(Bi, Al)] were investigated at 4.2 K. The LO-phonon replicas of free excitons emission line dominate in cathode-luminescence spectra of the samples heat treated in Bi followed by water quenching. The lines of bound excitons series, nLOI ds −, 1 , were observed in the emission of all samples, including the original ones. It was found that plasmon replicas are not proper only for nLOI s −1 lines, but, also, for nLOI d −1 lines. The weak exciton-plasmon coupling is manifested in one plasmon Stokes side band shoulders of nLOI d −1 lines. It is developed the theory of bound excitons multi-quantum optical transitions with participation of mixed plasmon-phonon oscillation modes. This theory allows for the calculation of the emission spectra form–function, without using any model. The theoretical spectra are in agreement with the experimental data.
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    Multiplasmon laser gain spectra of quantum wells [Articol]
    (2005) Klyukanov, Alexandr; Gurau, Virginia
    Results of computer simulations concerning gain spectra of In0.05Ga0.95As quantum wells are presented. A novel multi-plasmon concept of a light absorption and laser gain of low- dimensional structures is comprehensively discussed. A generalized theory of multi-plasmon optical transitions in direct gap quantum wells is developed using the cumulant expansion method and fluctuation-dissipation theorem. Multi-quantum LO-phonon-plasmon optical transitions are investigated with account on coherent memory effects in quantum wells. It is shown that a red shift of the absorption edge can be caused not only by the well-known mechanism of band gap shrinkage but also by multi-plasmon transitions. The comparison with other theories and experimental data measured in In0.05Ga0.95As quantum wells is given.
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    Hartree-fock Semiconductor Bloch Equations and charge density correlations [Articol]
    (2002) Klyukanov, Alexandr; Loiko, Natalia; Babushkin, Ihar; Gurau, Virginia
    Generalized Semiconducor Bloch Equations are derived with using the fluctuation-dissipation theorem. Four op- erator expectation values like density-density correlators are calculated with account of coherent memory effects. Interactionswith mixed plasmon-phonons modes and excitonic effects are taken into account. Comparison with different other theoretical approaches is provided. Numerical calculations of the spontaneous radiationproduced by interband multiplasmon recombination of electron-hole pairs are fulfilled in dependence on the temperatureand plasmaconcentration. It is shown that the intensity maximum of spontaneous radiationshifted to the region of the first LO-phonon satellite with increasing of concentration in accordance with experiments [19,21].
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    Laser gain spectra of quantum wells and multiplasmon optical transitions [Articol]
    (2005) Gurau, Virginia
    A novel multi-plasmon concept of a light absorption and laser gain of low- dimensional structures are comprehensively discussed. A Generalized Semiconductor Bloch Equations are derived with account of multi-plasmon optical transitions in direct gap quantum wells, using the cumulant expansion method and fluctuation-dissipation theorem. We present results of computer simulations concerning gain spectra of In 0.05Ga0.95As quantum wells with account of multi-plasmon optical transitions in two- dimensional systems.Multi -quantum LO-phonon-plasmon optical transitions are investigated with account of coherent memory effects in quantum wells. It is shown that a red shift of the absorption edge can be caused, not only by known mechanism of band gap shrinkage, but also by multi-plasmon transitions. The electron-hole plasma properties in the active region of the laser device and its interaction with the optical field are studied on a microscopic level using obtained Generalized Semiconductor Bloch Equations.The comparison with other theories and experimental data measured in In0.05Ga0.95As quantum wells is performed. The gain value g=50 cm-1 in 8 nm In 0.05Ga0.95As quantum wells is obtained at a surface density of electrons nd0=1.64 10-12 cm-2.