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  • 1. Crnjanski, J. V.
    et al.
    Gvozdić, Dejan M.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101).
    Intersubband absorption in modulation-doped V-shaped quantum wires2005In: NUSOD '05 - Proceedings of the 5th International Conference on Numerical Simulation of Optoelectronic Devices, 2005, p. 15-16Conference paper (Refereed)
    Abstract [en]

    The calculation of the intersubband absorption in a modulation-doped V-shaped-quantum-wire (V-QWR) is presented. The method is based on self-consistent solving of the single band Schrödinger equation in a nonparabolic approximation. Our calculation shows that the absorption spectrum is anisotropic and has two absorption peaks at 19meV and 115 meV depending on light polarization.

  • 2.
    Ekenberg, Ulf
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101). University of Belgrade, Serbia.
    Gvozdíc, Dejan M.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101). University of Belgrade, Serbia.
    Spin splitting in modulation-doped semiconductor quantum wells2009In: Quantum Wells: Theory, Fabrication and Applications, Nova Science Publishers, Inc., 2009, p. 385-425Chapter in book (Refereed)
    Abstract [en]

    We review different ways to achieve a spin splitting of two-dimensional electron and hole subbands with the combination of inversion asymmetry and spin-orbit interaction. In particular we focus on novel mechanisms to achieve a substantial spin splitting with a small applied bias across the sample. We discuss the proper inclusion of electric-field-induced spin splittings in the framework of the envelope function approximation and argue that the Rashba effect should be included in the form of a macroscopic potential as diagonal terms in a multiband approach rather than commonly used terms dependent on k and electric field. One of our findings is that the expectation values of the electric field can differ substantially and even have opposite signs for the spin-split components of a subband. Thus the frequent assignment of one expectation value to a subband is sometimes not appropriate. We also discuss symmetric quantum wells with Dresselhaus terms and the influence of the interfaces on the spin splitting. Our approach is applied to wide modulation-doped n-type InGaSb quantum wells with strong built-in electric fields in the interface regions. We demonstrate an efficient mechanism for switching on and off the Rashba splitting with an electric field being an order of magnitude smaller than the local built-in field that determines the Rashba splitting. For a slightly asymmetric quantum well we demonstrate a reversal of the spin direction in a spin subband in two steps as the in-plane wave vector is increased a little. Our most significant results pertain to the superefficient Rashba effect for holes. With a careful design of doping profile and strain we find that the wave vector splitting for hole subbands can be made several thousand times stronger than for electrons at the same electric field. The implications of our findings for spintronic devices, in particular the Datta-Das spin transistor and proposed modifications of it, are discussed.

  • 3.
    Gvozdic, Dejan
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Dynamic response of V-groove quantum wire laser2005In: Physics and Simulation of Optoelectronic Devices XIII / [ed] Osinski, M; Henneberger, F; Amano, H, BELLINGHAM, WA: SPIE-INT SOC OPTICAL ENGINEERING , 2005, Vol. 5722, p. 80-89Conference paper (Refereed)
    Abstract [en]

    The dynamic characteristics of an InGaAs/InP lattice-matched V-groove quantum wire laser are theoretically considered. The differential gain of the laser is derived from the k-p theory, taking into account nonparabolicity of both bands, the conduction and the valence band. We investigate the bandwidth of the laser versus its optical confinement, driving current and roll-off time, including nonlinear gain suppression. In spite of solid differential gain and the D-factor comparable with the best-performance QW laser, the maximum bandwidth of the laser is limited to about 20GHz due to insufficient optical confinement.

  • 4.
    Gvozdic, Dejan
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Ekenberg, Ulf
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Strong enhancement of Rashba effect in strained p-type quantum wells2005In: Physics of Semiconductors, Pts A and B / [ed] Menendez, J; VanDeWalle, CG, MELVILLE: AMER INST PHYSICS , 2005, Vol. 772, p. 1423-1424Conference paper (Refereed)
    Abstract [en]

    One of the most studied spintronic devices is the spin transistor proposed by Datta and Das. The mechanism behind this transistor is the Rashba effect: The inversion asymmetry caused by the gate voltage gives rise to a spin splitting. We show that the relevant spin splitting in k-space is typically two orders of magnitude larger in unstrained p-type quantum wells compared to n-type quantum wells. We also show that further order-of-magnitude improvement can be obtained by utilizing the frequently ignored lattice-mismatch between GaAs and AlGaAs.

  • 5.
    Gvozdic, Dejan M.
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Ekenberg, Ulf
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Beyond the Rashba model2006In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 32, no 02-jan, p. 458-461Article in journal (Refereed)
    Abstract [en]

    We analyze some common approximations made in connection with the Rashba effect, where a macroscopic electric field gives rise to a spin splitting. We demonstrate that the size of the Rashba splitting is not given by the expectation value of the electric field or some other average electric field, as is commonly assumed. Instead we find that the local electric field near an interface of a wide asymmetric modulation-doped quantum well can give rise to a Rashba splitting that is an order of magnitude larger than expected from the average electric field. The localization of the wave functions of the spin subbands can be quite sensitive to the parallel wave vector. Clear deviations from an energy-independent wave vector splitting occur when nonparabolicity is taken into account.

  • 6.
    Gvozdic, Dejan M.
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Ekenberg, Ulf
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Investigation of the super-efficient Rashba effect by simulation of Shubnikov-de Haas oscillations in a two-dimensional hole gas2006In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 34, no 02-jan, p. 377-380Article in journal (Refereed)
    Abstract [en]

    The Shubnikov-de Haas effect is frequently used for two-dimensional systems to determine individual subband populations, e.g. when the subbands are split by the Rashba effect. We have previously shown that the Rashba effect can give a wave vector splitting for holes that is up to three orders of magnitude larger than for electrons at the same electric field. To reach the optimum we have made a careful design of a modulation-doped quantum well with a top gate in which the negative differential Rashba effect is utilized. From the calculated hole Landau levels we determine the density of states at the Fermi energy and demonstrate a clear difference between the symmetric case without bias and the asymmetric case with a gate voltage of 100 meV, where the spin subband populations differ by a factor 3.

  • 7.
    Gvozdic, Dejan M.
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Schlachetzki, A
    Modulation response of V-groove quantum-wire lasers2005In: IEEE Journal of Quantum Electronics, ISSN 0018-9197, E-ISSN 1558-1713, Vol. 41, no 6, p. 842-847Article in journal (Refereed)
    Abstract [en]

    We analyze the modulation speed of an InGaAs-InP quantum-wire laser of a V-groove-shaped structure. The bandwidth is affected by the optical confinement Gamma, exhibiting a maximum at Gamma = 0.016. The maximum bandwidth for the intrinsic device is 20 GHz as a result of a calculation based on the experimentally obtained cross section of the device and including the nonparabolicity of the conduction and valence bands. We discuss the reduction of the bandwidth of the device itself by summarily considering the influence of the roll-off time and the cavity length as well as the nonlinear gain suppression.

  • 8.
    Gvozdić, Dejan M.
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101). University of Belgrade, Serbia.
    Ekenberg, Ulf
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101).
    Novel mechanism for order-of-magnitude enhancement of rashba effect in wide modulation-doped quantum wells2007In: Physics of Semiconductors: 28th International Conference on the Physics of Semiconductors - ICPS 2006, American Institute of Physics (AIP), 2007, p. 1371-1372Conference paper (Refereed)
    Abstract [en]

    The Rashba effect leading to subband splitting in quantum wells is frequently taken to be proportional to some average electric field. We here show that taking the spatial variation of the electric field into account gives important effects. In particular we demonstrate that one can apply a moderate electric field to a wide modulation-doped quantum well and get an order-of-magnitude enhancement of the Rashba splitting characteristic of the built-in interface field. For small asymmetry the wave function localization and spin projection of a subband can be rapid functions of the in-plane wave vector.

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