| 1. |
- Antonyuk, Vadim, et al.
(författare)
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Effect of electron-phonon interaction on electron conductance in one-dimensional systems
- 2004
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 69:15
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the effect of electron-phonon interaction on the electronic transport in a one-dimensional wire where both electrons and phonons are quantum confined. We found substeps appeared in the quantized electron conductance, and the step height depends on the electron-phonon coupling strength. With increasing temperature, the substep structure smooths out. Dependent on the transmission probability through the wire, this substep correction can be either positive or negative. In the limiting cases we reproduce the existing results.
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| 2. |
- Antonyuk, Vadim, et al.
(författare)
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Phonon transmission in III-V semiconductor superlattices and alloys
- 2005
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 20:5, s. 347-352
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Tidskriftsartikel (refereegranskat)abstract
- We have used the transfer matrix approach to investigate the LA phonon transmission along the [0 0 1] growth direction in GaAs/GaAlAs superlattices and in Ga1-xAlxAs alloys. Our calculated minigap in the phonon dispersion induced by the zone folding matches reasonably to the phonon filtering experiment. However, in the regime of phonon ballistic transport, we found insignificant effect of zone folding on phonon thermal conductance. On the other hand, the alloy scatterings largely suppress the phonon transmission probability and so lower the phonon thermal conductance of alloys.
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| 3. |
- Blom, Anders, et al.
(författare)
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Donor states in modulation-doped Si/SiGe heterostructures
- 2003
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 68:16: 165338
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Tidskriftsartikel (refereegranskat)abstract
- We present a unified approach for calculating the properties of shallow donors inside or outside heterostructure quantum wells. The method allows us to obtain not only the binding energies of all localized states of any symmetry, but also the energy width of the resonant states which may appear when a localized state becomes degenerate with the continuous quantum well subbands. The approach is nonvariational, and we are therefore also able to evaluate the wave functions. This is used to calculate the optical absorption spectrum, which is strongly nonisotropic due to the selection rules. The results obtained from calculations for Si/Si1-xGex quantum wells allow us to present the general behavior of the impurity states, as the donor position is varied from the center of the well to deep inside the barrier. The influence on the donor ground state from both the central-cell effect and the strain arising from the lattice mismatch is carefully considered.
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| 4. |
- Blom, Anders, et al.
(författare)
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Resonant states in doped quantum wells
- 2003
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Ingår i: Physica Status Solidi. B: Basic Research. - : Wiley. - 0370-1972. ; 235:1, s. 85-88
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Tidskriftsartikel (refereegranskat)abstract
- Resonant states can have an important influence on the electronic transport, noise and optical properties of heterostructure devices. We have used a non-variational method to study the resonant states formed by shallow donors inside and outside of quantum wells. The method allows us the evaluation of the position and the width (lifetime) of the resonant states and also of matrix elements such as optical transition probabilities. When the width is compared to results from the approach of resolvent operators, a quantitative difference is found, which we attribute to the neglected intraband scattering in the latter method. We also show how the impurity states, localized and resonant, evolve as the donor is moved into the quantum well from an originally infinite distance.
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| 5. |
- Blom, Anders, et al.
(författare)
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Resonant states induced by impurities in heterostructures
- 2002
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 65:15
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Tidskriftsartikel (refereegranskat)abstract
- A study of the formation of resonant states in the conduction band, induced by impurities outside heterostructure quantum wells, is presented. We derive general expressions for the capture and scattering amplitudes, the resonance position and width, and we also calculate the effect on the energy spectrum and the density of states in the quantum well. The theory is applied to two typical impurity potentials, the zero-range potential of deep levels and the Coulomb potential. It is found that the perturbation of the density of states can be significant over wide energy intervals, and that the resonance position may behave nonmonotonically with the modulation-doping distance. The resonance width decays exponentially with the distance, but becomes of the same order as the band discontinuity as we approach close to the quantum well interface. The capture and scattering coefficients may vary by several orders of magnitude over narrow energy intervals, producing a pronounced and strong scattering mechanism.
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| 6. |
- Chang, CH, et al.
(författare)
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Spin relaxation dynamics of quasiclassical electrons in ballistic quantum dots with strong spin-orbit coupling
- 2004
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 70:24
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Tidskriftsartikel (refereegranskat)abstract
- We performed path integral simulations of spin evolution controlled by the Rashba spin-orbit interaction in the semiclassical regime for chaotic and regular quantum dots. The spin polarization dynamics have been found to be strikingly different from the D'yakonov-Perel' (DP) spin relaxation in bulk systems. Also an important distinction has been found between long time spin evolutions in classically chaotic and regular systems. In the former case the spin polarization relaxes to zero within relaxation time much larger than the DP relaxation, while in the latter case it evolves to a time independent residual value. The quantum mechanical analysis of the spin evolution based on the exact solution of the Schrodinger equation with Rashba SOI has confirmed the results of the classical simulations for the circular dot, which is expected to be valid in general regular systems. In contrast, the spin relaxation down to zero in chaotic dots contradicts what has to be expected from quantum mechanics. This signals on the importance of quantum effects missed in the semiclassical simulations for long time spin dynamics.
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| 7. |
- Chang, CH, et al.
(författare)
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Spin transmission through quantum dots with strong spin-orbit interaction
- 2004
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Ingår i: Physics Letters. Section A: General, Atomic and Solid State Physics. - : Elsevier BV. - 0375-9601. ; 326:5-6, s. 436-441
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Tidskriftsartikel (refereegranskat)abstract
- Quantum oscillations of the spin conductance through regular and chaotic 2D quantum dots under the varying Rashba spin-orbit interaction and at zero magnetic field have been investigated numerically by summing up the spin evolution matrices for classical transmitting trajectories. The Fourier analysis of these oscillations indicates a strong geometry dependence of the power spectra. The spectra for narrow rings are dominated by a single peak as previous analytic result, for regular quantum dots are represented by multiple peaks, and for chaotic quantum dots by quasi-continuum peaks.
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| 8. |
- Chao, Koung-An, et al.
(författare)
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Energy transport in one-dimensional thermoelectric systems
- 2006
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Ingår i: Solid State Communications. - : Elsevier BV. - 1879-2766 .- 0038-1098. ; 139:9, s. 490-492
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Tidskriftsartikel (refereegranskat)abstract
- The efficiency of thermoelectric power generators and the coefficient of performance of thermoelectric refrigerators increase rapidly in the region of small ZT, and then level off to a flat curve in the region of large ZT, where ZT is the figure of merit. Therefore, simply because one-dimensional thermoelectric materials have high ZT predicted theoretically does not imply that efficient thermoelectric devices can be built with such one-dimensional systems. Our numerical analysis, based on the fundamental thermodynamics which is independent of material systems, with emphasis on energy transport has confirmed this conjecture. (c) 2006 Elsevier Ltd. All rights reserved.
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| 9. |
- Chao, Koung-An, et al.
(författare)
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Room-temperature semiconductor heterostructure refrigeration
- 2005
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 87:2
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Tidskriftsartikel (refereegranskat)abstract
- With the proper design of semiconductor tunneling barrier structures, we can inject low-energy electrons via resonant tunneling, and take out high-energy electrons via a thermionic process. This is the operation principle of our semiconductor heterostructure refrigerator (SHR) without the need of applying a temperature gradient across the device. Even for the bad thermoelectric material AlGaAs, our calculation shows that at room temperature, the SHR can easily lower the temperature by 5 - 7 K. Such devices can be fabricated with the present semiconductor technology. Besides its use as a kitchen refrigerator, the SHR can efficiently cool microelectronic devices.
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| 10. |
- Han, P, et al.
(författare)
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Analysis of optothermionic refrigeration based on semiconductor heterojunction
- 2006
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 99:7
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Tidskriftsartikel (refereegranskat)abstract
- We have examined the theory of optothermionic refrigeration combining the ideas of laser cooling and thermionic cooling [Mal'shukov and Chao, Phys. Rev. Lett. 86, 5570 (2001)] and its estimation on thermal energy extraction by using self-consistent calculations with the drift-diffusion model in this paper. Both the Auger and the Shockley-Read-Hall dissipation processes are considered. For GaAs/AlGaAs systems with various impurity concentrations and different widths of quantum well, it is found that the optothermionic cooler can extract thermal energy at a rate as much as 10 W/cm(2). The information to perform optothermionic refrigeration in real devices have also been provided. (c) 2006 American Institute of Physics.
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