| 1. |
- 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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| 2. |
- 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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| 3. |
- Lankinen, A., et al.
(författare)
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Dislocations at the interface between sapphire and GaN
- 2008
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Ingår i: Journal of materials science. Materials in electronics. - : Springer Science and Business Media LLC. - 0957-4522 .- 1573-482X. ; 19:2, s. 143-148
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Tidskriftsartikel (refereegranskat)abstract
- GaN layers grown by metal organic vapour phase epitaxy on sapphire were imaged by synchrotron radiation X-ray topography. The threading dislocations could not be resolved in the topographs due to their high density, but a smaller density of about 10(5) cm(-2) defects were seen in the interface between GaN and sapphire by utilizing large-area back-reflection topography for the sapphire substrates. The misfit dislocation images in the topographs form a well-resolved cellular network, in which the average cell size is roughly 30 mu m. Different cell shapes in the misfit dislocation networks are observed on different samples. Also, images of small-angle grains of similar size were found in transmission section topographs of the GaN layers.
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| 4. |
- Tarakanov, Yu. A., et al.
(författare)
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Scattering-assisted terahertz gain in semiconductor superlattices in the Wannier-Stark-Ladder regime
- 2006
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 74:12
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Tidskriftsartikel (refereegranskat)abstract
- Using the second-order perturbation theory we have calculated the scattering assisted gain spectra in GaAs/AlGaAs superlattice under a strong applied electric field in the Wannier-Stark-Ladder (WSL) regime. Nonequilibrium distribution function of quasi-two-dimensional carriers localized in each WSL level and indirect optical transitions between neighboring WSL levels accompanied by the emission or absorption of acoustical phonons are taken into account in our theoretical analysis and numerical calculation. We have shown that the experimentally observed down shift of the zero-gain frequency from the Bloch oscillation frequency is due to the inelastic nature of the phonon scattering and the formation of excitons when electron-hole pairs are photoexcited. Our theoretical results agree well with the experimental data which were obtained from analyzing the THz response of superlattices to the picosecond optical pulse excitation.
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| 5. |
- Vettchinkina, Valeria, et al.
(författare)
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The Monte Carlo method applied to carrier transport in Si/SiGe quantum wells
- 2005
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 19:21, s. 3353-3377
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Tidskriftsartikel (refereegranskat)abstract
- We present a complete Monte Carlo simulation of the transport properties of a Si/SiGe quantum well. The scattering mechanisms, viz. intervalley phonons, acoustic phonons, interface roughness and impurity scattering (including resonant scattering), are considered in detail, and we derive analytic expressions for the scattering rates, in each case properly taking the quantized electron wave functions into account. The numerically obtained distribution function is used to discuss the influence of each scattering mechanism for different electric fields applied parallel to the interfaces and also different temperatures.
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