| 1. |
- Ekenberg, Ulf, et al.
(författare)
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Control of spontaneous spin splitting in an asymmetric quantum well with the use of strain and/or magnetic field
- 2001
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - 1386-9477 .- 1873-1759. ; 10:03-jan, s. 81-85
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Tidskriftsartikel (refereegranskat)abstract
- Spin-orbit coupling combined with inversion asymmetry gives rise to spin splitting even in the absence of an applied magnetic field. The size of this spin splitting can be controlled by changing the degree of asymmetry using a gate voltage. We present here other less obvious ways of controlling the spontaneous spin splitting in a two-dimensional hole gas, where these effects are particularly large. Applying moderate stress can easily decrease the spin splitting by an order of magnitude. The mechanism is the strain-induced energy shift of the heavy-hole and light-hole subbands, which diminishes the degree of band mixing, which is found to be strongly correlated to the spin splitting. An applied magnetic field causes an additional Zeeman splitting, but we find that a magnetic field of 1T can be sufficient to practically erase the difference between a symmetric quantum well (without subband splitting) and an asymmetric quantum well. We have simulated Shubnikov-de Haas oscillations and found that two periodicities in 1/B can occur even for one filled spin-degenerate hole subband.
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| 2. |
- Holmstrom, P., et al.
(författare)
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Proposal of an optical modulator based on resonant tunneling and intersubband transitions
- 2001
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Ingår i: IEEE Journal of Quantum Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9197 .- 1558-1713. ; 37:2, s. 224-230
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Tidskriftsartikel (refereegranskat)abstract
- We propose and analyze an optical modulator based on intersubband transitions. The absorption is modulated by modulating the carrier density in the ground state of a quantum well (QW). Electrons are injected resonantly into this subband from a QW reservoir subband through a single barrier. When the two states are tuned out of resonance, the electrons are rapidly evacuated by means of the optical held, A waveguide based on surface plasmons is assumed in order to have a high optical mode overlap. Calculations are performed for a cascaded structure with four periods, assuming InGaAs-InAlAs QWs, The considered modulator structure operates at lambda =6.0 mum and is RC limited to 27 GHz, An extinction ratio of it is obtained with a low applied voltage of 0.6 V, At larger applied voltages, the absorption is bistable, Absorption at shorter/longer wavelengths can be obtained by using materials with a larger/smaller conduction band offset. We also assess resonant tunneling from a 2-D electron gas reservoir into an array of quantum dots and compare it to the 2-D-2-D tunneling resonance.
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| 3. |
- Holmström, Petter, et al.
(författare)
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Design of intersubband optical modulators
- 2002
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Ingår i: Proceedings of the 26th International Conference on the Physicsof Semiconductors (26th ICPS), Edinburgh, Scotland, 2002. ; , s. P126-
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Konferensbidrag (refereegranskat)
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| 4. |
- Jänes, Peter, et al.
(författare)
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A high-speed intersubband modulator based on quantum interference in double quantum wells
- 2002
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Ingår i: IEEE Journal of Quantum Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9197 .- 1558-1713. ; 38:2, s. 178-184
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Tidskriftsartikel (refereegranskat)abstract
- Calculations on a modulator based on quantum interference in AlGaAs/GaAs asymmetric double quantum wells (QWs) are performed. The modulation of the absorption is based on the anti-crossing behavior of the two lowest states in the coupled wells. At anti-crossing, the oscillator strengths of the transitions from these two lowest states to a higher state are changed in opposite directions. The width of the barrier between the wells should be thick enough to allow a large change in oscillator strength with applied field, yet thin enough so that the absorption peaks of the transitions are resolved. The QWs are designed so that one absorption peak has only a small energy shift for the transition used for modulation while the absorption varies rapidly with the applied voltage. A complete structure including a surface plasmon waveguide is proposed enabling calculations of modal absorption. Parameters important for the performance of the modulator are then determined. An extinction ratio of 10 dB at a wavelength of 8.4 mum is predicted for a device length of 18 mum and a peak-to-peak voltage of 0.9 V. The resistance-capacitance-limited 3-dB bandwidth is 130 GHz. The predicted performance compares very favorably with present interband modulators based on the quantum-confined Stark effect.
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| 5. |
- Malkova, N., et al.
(författare)
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Spin properties of quantum wells with magnetic barriers. I. A k center dot p analysis for structures with normal band ordering
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:15
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Tidskriftsartikel (refereegranskat)abstract
- The electronic band-edge spectrum of magnetic semiconductor quantum wells containing a diluted magnetic semiconductor as one of the constituents is studied within the envelope-function formalism. The effects of Mn d electrons are explicitly included in a k.p Hamiltonian which in the first approximation of perturbation theory is shown to be reduced to an effective Kane model. The sp-d hybridization leads to a spin-splitting effect. The results are applied to the system Cd1-xMnxTe/CdTe. The spin-splitting effect is studied as a function of external magnetic field, well width, valence band offset and fraction of the magnetic atoms. The numerical results are in accord with experimental data.
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| 6. |
- Malkova, N., et al.
(författare)
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Spin properties of quantum wells with magnetic barriers. II. Inverted band ordering and spin polarized interface states
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:15
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Tidskriftsartikel (refereegranskat)abstract
- The electronic band-edge spectrum of the interface states in the magnetic semiconductor quantum wells based on narrow-gap semiconductors with mutually inverted band arrangement is studied within the envelope-function formalism. Interface states are shown to appear in these structures in the case of overlapping bulk bands of the constituents. The hybridization between the bare sp-electron states and the d states of the Mn atoms leads to spin splitting. The spin-splitting effect of the interface states as a function of external magnetic field, well width, band offsets, and fraction of the magnetic atoms, is studied. One essential result is that one can design a structure where the states localized at the interfaces only have one spin direction. The results give evidence of the perspective for using the magnetic semiconductor structures in spin electronics.
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| 7. |
- Mauritz, O., et al.
(författare)
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Magnetic-field-induced suppression of spontaneous spin-splitting of hole subbands
- 2000
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - 1386-9477 .- 1873-1759. ; 6:04-jan, s. 779-782
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Tidskriftsartikel (refereegranskat)abstract
- The spin-splitting in the valence band in an InxGa1-xAs/InxGa1-xAsyP1-y quantum well is investigated theoretically using a 6 x 6 Luttinger-Kohn Hamiltonian. We compare the Landau levels in a perpendicular magnetic field with the corresponding results for the subband dispersion;. It is shown that the asymmetry of the quantum well has a very small impact on the Landau level splitting for B > 1 T in sharp contrast to the subbands in the absence of a magnetic field. The significance of our findings on the interpretation of Shubnikov-de Haas experiments is discussed.
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