| 1. |
- 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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| 2. |
- 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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| 3. |
- Jin, Kui-Juan, et al.
(författare)
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Terahertz frequency radiation from Bloch oscillations in GaAs/Al0.3Ga0.7As superlattices
- 2003
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 68:15: 153315
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Tidskriftsartikel (refereegranskat)abstract
- We have performed a joint theoretical and experimental study to investigate the terahertz radiation from Bloch oscillations in a GaAs/Al0.3Ga0.7As superlattice under the condition that there is no Zener tunneling. The total radiation intensity has been calculated with a semiclassical approach in the low field regime where the Wannier-Stark ladder (WSL) cannot be resolved, and with an exact numerical solution in the high field regime where the WSL is well formed. With an adjustment of the intensity units, without fitting material parameters, the calculated results agree almost perfectly with the measured data given in arbitrary units. Consequently, our work gives convincing evidence that the measured THz radiation is due to the Bloch oscillations.
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| 4. |
- Larsson, Marcus, et al.
(författare)
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Thermopower anomaly in multiple barrier structures
- 2003
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 68:23: 233302
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Tidskriftsartikel (refereegranskat)abstract
- We have predicted that in suitable multiple barrier structures without applied bias, the thermopower may change sign because of quantum transport process. We have performed detailed numerical calculation to show that the predicted thermopower anomaly can be experimentally observed. This thermopower anomaly does not violate thermodynamic laws.
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| 5. |
- Luo, GL, et al.
(författare)
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Growth of high-quality Ge epitaxial layers on Si(100)
- 2003
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Ingår i: Japanese Journal of Applied Physics. - 0021-4922. ; 42:5B, s. 517-519
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Tidskriftsartikel (refereegranskat)abstract
- A method of growing high-quality epitaxial Ge layers on a Si(100) substrate is reported. In this method, a 0.8 mum Si0.1Ge0.9 layer was first grown. Due to the large lattice mismatch between this layer and the Si substrate, many dislocations form near the interface and in the lower part of the Si0.1Ge0.9 layer. A 0.8 mum Si0.05Ge0.95 layer and a 1.0 mum top Ge layer were subsequently grown on the Si0.1Ge0.9 layer. The formed interfaces of Si0.05Ge0.95/Si0.1Ge0.9 and Ge/Si0.05Ge0.95 can bend and terminate the upward-propagated dislocations very effectively. The in situ annealing process was also performed for each individual layer. Experimental results show that the dislocation density in the top Ge layer can be greatly reduced, and the surface is very smooth, while the total thickness of the structure is only 2.6 mum.
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| 6. |
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| 7. |
- Mal'shukov, AG, et al.
(författare)
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Spin-current generation and detection in the presence of an ac gate
- 2003
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 68:23
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Tidskriftsartikel (refereegranskat)abstract
- We predict that in a narrow gap III-V semiconductor quantum well or quantum wire, an observable electron spin current can be generated with a time-dependent gate to modify the Rashba spin-orbit coupling constant. Methods to rectify the so generated ac current are discussed. An all-electric method of spin-current detection is suggested, which measures the voltage on the gate in the vicinity of a two-dimensional electron gas carrying a time-dependent spin current. Both the generation and detection do not involve any optical or magnetic mediator.
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| 8. |
- Shimada, Y, et al.
(författare)
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Terahertz conductivity and possible Bloch gain in semiconductor superlattices
- 2003
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Ingår i: Physical Review Letters. - 1079-7114. ; 90:4: 046806
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated terahertz emission due to dynamical electron transport in wide-miniband GaAs/Al0.3Ga0.7As superlattices. By noting that the time-domain THz emission spectroscopy inherently measures the step-response of the electron system to the bias electric field, the obtained THz spectra were compared with the high-frequency conductivities predicted for miniband transport. Excellent agreement between theory and experiment strongly supports that the THz gain due to Bloch oscillating electrons persists at least up to 1.7 THz. It was also found that Zener tunneling into the second miniband sets the high-frequency limit to the THz gain for the samples studied here.
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