| 1. |
- Romanelli, F, et al.
(författare)
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Overview of the JET results
- 2011
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 51:9
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Tidskriftsartikel (refereegranskat)abstract
- Since the last IAEA Conference JET has been in operation for one year with a programmatic focus on the qualification of ITER operating scenarios, the consolidation of ITER design choices and preparation for plasma operation with the ITER-like wall presently being installed in JET. Good progress has been achieved, including stationary ELMy H-mode operation at 4.5 MA. The high confinement hybrid scenario has been extended to high triangularity, lower ρ*and to pulse lengths comparable to the resistive time. The steady-state scenario has also been extended to lower ρ*and ν*and optimized to simultaneously achieve, under stationary conditions, ITER-like values of all other relevant normalized parameters. A dedicated helium campaign has allowed key aspects of plasma control and H-mode operation for the ITER non-activated phase to be evaluated. Effective sawtooth control by fast ions has been demonstrated with3He minority ICRH, a scenario with negligible minority current drive. Edge localized mode (ELM) control studies using external n = 1 and n = 2 perturbation fields have found a resonance effect in ELM frequency for specific q95values. Complete ELM suppression has, however, not been observed, even with an edge Chirikov parameter larger than 1. Pellet ELM pacing has been demonstrated and the minimum pellet size needed to trigger an ELM has been estimated. For both natural and mitigated ELMs a broadening of the divertor ELM-wetted area with increasing ELM size has been found. In disruption studies with massive gas injection up to 50% of the thermal energy could be radiated before, and 20% during, the thermal quench. Halo currents could be reduced by 60% and, using argon/deuterium and neon/deuterium gas mixtures, runaway electron generation could be avoided. Most objectives of the ITER-like ICRH antenna have been demonstrated; matching with closely packed straps, ELM resilience, scattering matrix arc detection and operation at high power density (6.2 MW m-2) and antenna strap voltages (42 kV). Coupling measurements are in very good agreement with TOPICA modelling. © 2011 IAEA, Vienna.
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| 2. |
- Kaniewska, M., et al.
(författare)
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Hole emission mechanism in Ge/Si quantum dots
- 2011
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Ingår i: Physica Status Solidi (C) Current Topics in Solid State Physics. - : Wiley. - 1610-1642 .- 1862-6351. ; 8:2, s. 411 -413
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Tidskriftsartikel (refereegranskat)abstract
- The mechanisms determining emission of holes in self-assembled Ge quantum dots (QDs) embedded in the p-type Si matrix have been investigated. Specimens were prepared by molecular beam epitaxy (MBE). Electrical methods such as deep level transient spectroscopy (DLTS) and capacitance versus voltage (C-V) measurements were used for the study. The emission mechanisms were identified by measuring a QD-related signal as a function of the repetition frequency of the filling pulses with the reverse voltage and the pulse voltage as a parameter. An observed shift of the signal position or its absence versus the voltage parameters was interpreted in terms of thermal, tunnelling and mixed processes and attributed to the presence of a Coulomb barrier formed as a result of the charging effect. Thermal emission properties of the QDs were characterized under such measurement conditions that tunnelling contributions to the DLTS spectra could be neglected.
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| 3. |
- Kaniewska, M., et al.
(författare)
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Spatial variarion of hole eigen energies in Ge/Si quantum wells
- 2011
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Ingår i: AIP Conference Proceedings. - : AIP. - 1551-7616 .- 0094-243X. - 9780735410022 ; 1399, s. 293-294
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Konferensbidrag (refereegranskat)abstract
- Ge quantum well (QW) structures were prepared through Si-capping of 3.3 ML of Ge by MBE on p +-(001) Si substrates at a growth temperature of 550°C. The spatial variation of hole eigen energies in the QW were revealed by DLTS. Depending on the position on the wafer surface, the hole emission may be imposed by a lateral quantum confinement effect. Results of a study by HRTEM methods demonstrate pronounced fluctuations of the QW thickness and variations of the strain field in the QW.
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| 6. |
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| 7. |
- Kaczmarczyk, M., et al.
(författare)
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The influence of inhomogeneous trap distribution on results of DLTS study
- 2011
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Ingår i: Microelectronics and Reliability. - : Elsevier BV. - 0026-2714. ; 51:7, s. 1159-1161
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Tidskriftsartikel (refereegranskat)abstract
- A model is developed to describe how a narrow distribution of deep traps adjacent to quantum dots (QDs) influences the trap-related signals measured by frequency scanned deep level transient spectroscopy (FS-DLTS). By comparison with experiment, it is demonstrated that traps with a steep concentration gradient, positioned in the so called transition layer close to the edge of the depletion region ("lambda-effect"), have a strong influence on DLTS signal amplitudes. This is manifested by an extreme sensitivity to the change in the Fermi-level position when temperature is varied.
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| 8. |
- Kaniewska, M., et al.
(författare)
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Classification of Energy Levels in Quantum Dot Structures by Depleted Layer Spectroscopy
- 2010
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 1543-186X .- 0361-5235. ; 39:6, s. 766-772
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Tidskriftsartikel (refereegranskat)abstract
- The coexistence of quantum confined energy levels and defect energy levels in quantum dot (QD) structures may cause difficulties in distinguishing between their different origin when using deep-level transient spectroscopy (DLTS). Using InAs/GaAs QDs as demonstration vehicles, we present methodologies to obtain such a classification by DLTS. QD-related spectra measured as a function of repetition frequency of electrical pulses, f, or temperature, T, and reverse voltage, V (R), are depicted as contour plots on (f, V (R)) and (T, V (R)) planes, thus reflecting the complex thermal and tunneling emission of electrons from the ground and excited states. Defect-related levels give rise to different contour patterns and undergo modification, exhibiting double-peak structured emission when defects are agglomerated in the vicinity of the QD plane. This effect is interpreted in terms of an interaction between electron states in traps and the confined QD states.
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