| 1. |
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| 2. |
- Xu, Hongxing, et al.
(författare)
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Unified treatment of fluorescence and Raman scattering processes near metal surfaces
- 2004
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Ingår i: Physical Review Letters. - 1079-7114. ; 93:24
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Tidskriftsartikel (refereegranskat)abstract
- We present a general model study of surface-enhanced resonant Raman scattering and fluorescence focusing on the interplay between electromagnetic effects and the molecular dynamics. Our model molecule is placed close to two Ag nanoparticles and has two electronic levels. A Franck-Condon mechanism provides electron-vibration coupling. Using realistic parameter values for the molecule we find that an electromagnetic enhancement by 10 orders of magnitude can yield Raman cross sections sigma(R) of the order 10(-14) cm(2). We also discuss the dependence of sigma(R) on incident laser intensity.
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| 3. |
- Csontos, Dan, et al.
(författare)
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Characteristics of electron transport through vertical double-barrier quantum-dot structures: Effects of symmetric and asymmetric variations of the lateral confinement potentials
- 2002
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 66:20
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Tidskriftsartikel (refereegranskat)abstract
- We report on a theoretical study of the electron transport through laterally-confined, vertical double-barrier resonant-tunneling (DBRT) structures, defined as one-dimensional (1D)-0D-1D systems, with a tunable lateral confinement. The current and the differential conductance of the systems are calculated and the influence caused by varying the lateral confinement on the device characteristics is investigated. Three representative systems are studied. First of all, a 1D-0D-1D device, symmetric with respect to the current flow, with a variable lateral confinement in the double-barrier quantum-well (DBQW) region, is investigated. This device would in an experimental setup correspond to the structure in which a thin, lateral metallic gate is placed in the DBQW region. Subsequently, calculations are performed for two asymmetric 1D-0D-1D devices, in which the strongest, but varying, lateral confinement is placed either in the collector or in the emitter region. In experiments, these two devices would correspond to the situations where a lateral metallic gate is positioned below or on top of the DBQW structure. The calculations predict several phenomena for the device characteristics. It is shown that as the lateral confinement increases, in addition to those normally observed current onsets and pinch-offs that move toward higher bias voltages, several current onsets and pinch-offs move towards lower bias voltages. These negative shifts of the current onsets and pinch-offs with increasing of the lateral confinement have so far not been expected for gated DBRT devices. It is also found that the threshold voltages, at which the current onsets and pinch-offs appear, depend strongly on the strength and position of the lateral confinement and on the Fermi levels in the collector and the emitter. The models that explain these predictions are presented and discussed.
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| 4. |
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| 5. |
- Csontos, Dan, et al.
(författare)
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Quantum interference effects in electron transport through Y-branches
- 2002
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Ingår i: 7th International Conference on Nanometer-Scale Science and Technology and 21st European Conference on Surface Science.
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Konferensbidrag (refereegranskat)abstract
- Recently, nonlinear properties of three-terminal ballistic junctions (TBJs) were predicted by theoretical calculations done by Xu, and potential applications such as rectification and logic function proposed. In that analysis the TBJ was modeled by connecting three quantum point contacts via a ballistic cavity with adiabatic boundaries, thus neglecting any backscattering of electrons. In this paper we develop a realistic model based on the scattering-matrix method for the calculation of transport through TBJs with arbitrary potential profiles. Temperature-dependent linear and nonlinear transport has been calculated and analyzed for a number of Y-shaped devices with different geometries, sizes, impurity concentrations and various degrees of boundary roughness. Interference effects are shown to influence the characteristics of the calculated transport in a strong way at low temperature where new quantum phenomena are predicted
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| 6. |
- Csontos, Dan, et al.
(författare)
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Scattering-matrix formalism of electron transport through three-terminal quantum structures: formulation and application to Y-junction devices
- 2002
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 14:47, s. 12513-12528
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a formalism for the calculation of electron transport through three-terminal junction devices, which have received attention due to their recently demonstrated non-linear electrical properties. The formalism, which is based on the scattering-matrix method, takes quantum interference effects fully into account. Furthermore, the formalism provides numerical stability in the calculations as well as large flexibility in the modelling of arbitrary potential profiles due to the common basis approach used in the formulation. The method is used to calculate the transport properties for Y-shaped three-terminal ballistic junction (TBJ) structures with configurations typical of recently performed experiments. Quantum interference effects are shown to strongly influence the transport characteristics of TBJ structures due to complex scattering of the electrons in the cavity-like coupling window between the three arms of the device. The theoretical approach presented in this paper provides a flexible tool for the study of such quantum interference effects, which may play an important role in the design and functionality of future nanoscale devices based on three-terminal junctions.
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| 7. |
- Fasth, Carina, et al.
(författare)
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Effects of breaking current conservation on the phase properties of two-terminal quantum systems
- 2003
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Ingår i: Physica E: Low-Dimensional Systems and Nanostructures. - 1386-9477. ; 17:1-4, s. 579-583
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Tidskriftsartikel (refereegranskat)abstract
- We study the reflection and transmission phase properties of two-terminal quantum structures coupled to a third lead. The systems are effectively three-terminal and current conservation is broken with regard to the original two-terminal systems. Two structures, a waveguide with an attached stub quantum dot and a waveguide with an inline, double-barrier confined quantum dot, are considered. The transmission and reflection phase properties are calculated for these systems with different couplings to the third lead. The results show that the discontinuous phase shifts seen in the current-conserved two-terminal systems are removed when the third lead is attached. However, as long as the coupling between the quantum systems and the additional lead is weak, sharp but continuous phase drops within narrow energy ranges can still be clearly identified.
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| 8. |
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| 9. |
- Gustafson, Boel, et al.
(författare)
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Coupling between lateral modes in a vertical resonant tunneling structure
- 2002
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Ingår i: Physica E: Low-Dimensional Systems and Nanostructures. - 1386-9477. ; 13:2-4, s. 950-953
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Tidskriftsartikel (refereegranskat)abstract
- We present experimental results and theoretical calculations of the vertical electron transport through a laterally constricted resonant tunneling transistor. Current-voltage measurements at 4.2 K show numerous current peaks that exhibit a complex dependence on the applied gate voltage. A scattering-matrix approach combined with the Landauer formalism was used to perform quantum mechanical calculations of the electron transport through a quantum dot structure with laterally confined emitter and collector regions. The simulations qualitatively reproduce the measured data, suggesting a strong coupling between the lateral modes in the quantum dot and the collector
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| 10. |
- Junno, T, et al.
(författare)
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Single-electron tunneling effects in a metallic double dot device
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:4, s. 667-669
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Tidskriftsartikel (refereegranskat)abstract
- We report on differential conductance measurements on a gold double-dot structure at 4.2 K. The two dots were connected in series by tunnel junctions formed by atomic force microscopy manipulation of nanodisks. The tunnel junctions were made strongly asymmetric. The characteristic honeycomb-shaped charging diagram separating different Coulomb blockade regions of well-defined occupancy of electrons was observed and the cells in the charging diagram were found to be skewed by the asymmetry of the tunnel junctions. In addition, a double-dot Coulomb staircase structure, with steps of varying width, was observed and was studied for varying gate voltage. The occupancy of electrons on the two dots was determined as a function of both drain source and gate voltages.
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| 11. |
- Lewen, R., et al.
(författare)
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High frequency characterization of a GaInAs/InP electronic waveguide T-branch switch
- 2002
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91:4, s. 2398-2402
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Tidskriftsartikel (refereegranskat)abstract
- We report comprehensive microwave measurements on a T-branch switch; a GaInAs/InP electron waveguide based structure. The study includes a small signal model of the device where limitations of high frequency operation are discussed. An example of large signal operation where the nonlinearity of the device is exploited by operating the T-branch switch as a frequency multiplier is demonstrated.
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| 12. |
- Linke, H, et al.
(författare)
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Quantum ratchets and quantum heat pumps
- 2002
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Ingår i: Applied Physics A: Materials Science & Processing. - : Springer Science and Business Media LLC. - 1432-0630. ; 75:2, s. 237-246
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Tidskriftsartikel (refereegranskat)abstract
- Quantum ratchets are Brownian motors in which the quantum dynamics of particles induces qualitatively new behavior. We review a series of experiments in which asymmetric semiconductor devices of sub-micron dimensions are used to study quantum ratchets for electrons. In rocked quantum-dot ratchets electron-wave interference is used to create a non-linear voltage response, leading to a ratchet effect. The direction of the net ratchet current in this type of device can be sensitively controlled by changing one of the following experimental variables: a small external magnetic field, the amplitude of the rocking force, or the Fermi energy. We also describe a tunneling ratchet in which the current direction depends on temperature. In our discussion of the tunneling ratchet we distinguish between three contributions to the non-linear current-voltage characteristics that lead to the ratchet effect: thermal excitation over energy barriers, tunneling through barriers, and wave reflection from barriers. Finally, we discuss the operation of adiabatically rocked tunneling ratchets as heat pumps.
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| 13. |
- Maximov, Ivan, et al.
(författare)
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Nanoimprint lithography for fabrication of three-terminal ballistic junctions in InP/GaInAs
- 2002
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484. ; 13:5, s. 666-668
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Tidskriftsartikel (refereegranskat)abstract
- We present processing technology and characterization results for InP/GaInAs two-dimensional electron gas (2DEG) three-terminal ballistic junction (TBJ) devices manufactured using nanoimprint lithography (NIL). To transfer sub-100 nm features into a high-mobility InP-based 2DEG material, we used SiO2/Si stamps made using electron beam lithography and reactive ion etching. After NIL, the resist residues are removed in oxygen plasma; this is followed by wet etching of InP/GaInAs to define the TBJ structures. Fabricated TBJ devices are characterized using scanning electron microscopy and electron transport measurements. Highly non-linear electrical characteristics as predicted by the theory (Xu H Q 2001 APPI. Phys. Lett. 78 2064) are demonstrated.
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| 14. |
- Maximov, Ivan, et al.
(författare)
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Nanoimprint technology for fabrication of three-terminal ballistic junction devices in GaInAs/InP
- 2003
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Ingår i: Microelectronic Engineering. - 1873-5568. ; 67-8, s. 196-202
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Tidskriftsartikel (refereegranskat)abstract
- We present processing technology based on nanoimprint lithography (NIL) and wet etching for fabrication of GaInAs/InP three-terminal ballistic junction (TBJ) devices. To transfer sub-100 nm features into a high-mobility InP-based 2DEG material, we used SiO2/Si stamps made with electron beam lithography and reactive ion etching. After the NIL, the resist residues are removed in oxygen plasma followed by wet etching of GaInAs/InP to define the M-structures. Fabricated TBJ-devices are characterized using scanning electron microscopy and electron transport measurements. Highly non-linear electrical characteristics of the TBJ structures are demonstrated and compared with E-beam defined devices. (C) 2003 Elsevier Science B.V. All rights reserved.
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| 15. |
- Ouchterlony, Thomas
(författare)
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Electron Transport and Chaos in Model Mesoscopic Systems
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis mesoscopic structures intermediate in size between classical macroscopic objects and quantum mechanical objects as atoms are treated. The size of mesoscopic systems are of the same order as the wavelength of the electrons, which makes it necessary to take quantum mechanics into account. However the systems are much larger than atoms and molecules and provide a link between classical and quantum physics. These systems are very interesting both for understanding fundamental physics and technologically, since semiconductor components in about a decade will be small enough to make quantum mechanical effects important.The mesoscopic systems, or nanostructures as they are also called due to their size of about 10 - 1000 nm (nanometer), are fabricated from GaAs/ A1GaAs heterostructures. The A1GaAs is n-doped in order to create a two-dimensional electrongas (2DEG) between the GaAs and A1GaAs. Further constriction in the movement of the electrons are made by applying a gate voltage to the gate at the top of the heterostructure.Several different kinds of models for have been used to investigate different aspects of mesoscopic systems. The models are ranging from a basically onedimensional model calculating the conductance over a quantum point contact with an assumed linear potential drop to a realistic model for calculating the conductance through an arbitrary mesoscopic system knowing the gate structure and the physical structure of the heterostructure. In the latter model the potential in the 2DEG is calculated using a self-consistent Thomas-Fermi method and a hybrid recursive Green's function method uses this potential to yield the conductance.Other investigations made in this thesis are electron transport in quantum dots coupled in a deterministic aperiodic order and studies of chaos in mesoscopic systems. One interesting aspect of studying chaos in mesoscopic systems is that classical and quantum mechanical measures of chaos can be studied for the same system, which have been done here for several different smooth potentials. The weak localization peak for the conductance at low magnetic field has been suggested to be related to the underlying classical dynamics and here this is investigated and partially questioned. A recently suggested nearest neighbor energy level distribution for mixed regular and chaotic system, called semi-Poisson distribution, intermediate between the Poisson (regular) and Wigner ( chaotic) distributions have been found in fundamentally different systems. These systems are for a quantum dot with soft potential and in a quantum dot with spin-orbit coupling.
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| 16. |
- Persson, Martin, et al.
(författare)
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Electronic structure of [100]-oriented free-standing semiconductor nanowires
- 2004
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 4:12, s. 2409-2414
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Tidskriftsartikel (refereegranskat)abstract
- We report on a theoretical study of the electronic structure of [100]-oriented free-standing III-V semiconductor nanowires with quadratic (square wire) and rectangular (nanobelt) cross-sections based on an atomistic tight-binding approach. It is shown that at the same cross-section aspect ratio, the characteristics of the band structure and state wave functions of the nanowires in the vicinity of the band edges are insensitive to variation of the lateral size, although the band energies show a strong dependence on the lateral size. It is also shown that the effective mass of the conduction bands of the nanowires is systematically enhanced with decrease of the nanowire size, and k(.)p analysis generally overestimates the effective mass enhancement.
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| 17. |
- Persson, Martin, et al.
(författare)
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Electronic structure of nanometer-scale GaAs whiskers
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 81:7, s. 1309-1311
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Tidskriftsartikel (refereegranskat)abstract
- We report a theoretical study of the electronic structure of GaAs nanowhiskers, grown in the [111] direction with hexagonal cross section, based on a tight binding approach. It is shown that the band structure of the GaAs nanowhiskers shifts from a direct band gap to an indirect band gap when the lateral size of the nanowhiskers becomes smaller than a certain value. The effective masses of the electrons and holes are shown to increase with decreasing the nanowhisker lateral size. It is also shown that the light-hole states appear to be at the top of the valence bands. The electrical and optical properties of the nanowhiskers are discussed in terms of the results of the calculations. (C) 2002 American Institute of Physics.
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| 18. |
- Persson, Martin, et al.
(författare)
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Electronic structure of nanometer-scale semiconductor wires
- 2003
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Ingår i: 2003 Third IEEE Conference on Nanotechnology. IEEE-NANO 2003. Proceedings (Cat. No.03TH8700). - 0780379764 ; , s. 111-114
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Konferensbidrag (refereegranskat)abstract
- We report a theoretical study of the electronic structure and optical properties of GaAs nanowires grown in the [111] direction with a hexagonal cross section, based on a tight-binding approach. It is shown that in the nanowires the degeneracy of the light-hole and heavy-hole bands at the Γ-point seen in the bulk material is lifted, and the light-hole state is located above the heavy-hole state, in strong contrast to the prediction by effective mass theory. The imaginary part of the dielectric function of the nanowires is also calculated and the absorption spectra is found to be strongly polarized
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| 19. |
- Persson, Martin, et al.
(författare)
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Electronic structure of nanometer-sized semiconductor crystals
- 2002
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Ingår i: 7th International Conference on Nanometer-Scale Science and Technology and 21st European Conference on Surface Science.
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Konferensbidrag (refereegranskat)abstract
- We report on a theoretical study of the electronic structure of semiconductor nanocrystals, based on a tight-binding method. Both one- and zero-dimensional structures have been studied. Concerning the one-dimensional structures, the effect of the confinement on the band structure of nanowires has been studied. We find that a transition from direct to indirect band gap occurs in the band structure as the size of the wire becomes smaller than a critical size. The effect is particularly prominent in the GaAs material. In the case of the zero-dimensional nanocrystals we have studied the effect of the confinement on the electronic structure of silicon. We show that the six-fold degenerate conduction band minima of the Si bulk crystal split into an A1 state, an E state and a T2 state. The ordering of these states is found to change with the size of the nanocrystal. The wave functions of the lowest unoccupied states and the highest occupied states of each symmetry have also been analyzed
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| 20. |
- Persson, Martin, et al.
(författare)
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Giant polarization anisotropy in optical transitions of free-standing InP nanowires
- 2004
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 70:16
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Tidskriftsartikel (refereegranskat)abstract
- We report a theoretical study of the electronic structure and optical properties of free-standing semiconductor nanowires, based on an atomistic tight-binding approach. It is shown that the optical transition between the valence-band maximum and conduction-band minimum of an intrinsic nanowire is fully polarized along the wire axis, and this giant polarization anisotropy can be explained in terms of intrinsic band-structure properties of the nanowire. It is also predicted that the optical spectra and polarization ratio of the nanowire can be tuned with temperature and the chemical potential of carriers in the nanowire.
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| 21. |
- Persson, Martin, et al.
(författare)
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Theoretical study of electronic structure of silicon nanocrystals
- 2002
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Ingår i: Physica scripta. - 0031-8949 .- 1402-4896. ; T101, s. 147-150
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Konferensbidrag (refereegranskat)abstract
- We report on a theoretical study of the electronic structure of silicon nanocrystals with a shape of the regular rhombic dodecahedron, based on a tight-binding method. The energies of the lowest unoccupied state and the highest occupied state have been calculated. We have shown that the six-fold degenerate conduction band minima of the bulk silicon crystal are split into a non-degenerate A(1) state, a double-degenerate E state and a triple-degenerate T-2 state and that the ordering of the energies of these states depends on the size of the silicon nanocrystal. Thus the lowest unoccupied state of the silicon nanocrystal can have different symmetries at different nanocrystal sizes. However. as the size of the nanocrystal changes, the symmetry of the highest occupied state remains the same; it is T-2 symmetric. The wave functions of the lowest unoccupied and highest occupied states have also been calculated. It is shown that these states have very different localization properties. The wave function of the lowest unoccupied A(1) state is largely localized on the central atomic site and on its nearest neighbors. In contrast, the wave function of the lowest unoccupied E state has no contribution from the orbitals of the central atom. Furthermore, the wave functions of both the lowest unoccupied and the highest occupied T-2 states are distributed more evenly over a large portion of the silicon nanocrystals.
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| 22. |
- Shorubalko, Ivan, et al.
(författare)
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A novel frequency-doubling device based on three-terminal ballistic junction
- 2002
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Ingår i: Device Research Conference (Cat. No.02TH8606). - 0780373170 ; , s. 159-160
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Konferensbidrag (refereegranskat)abstract
- Summary form only given. Ballistic devices have received increasing attention for their nonlinear electrical properties, which are interesting from both physics and application points of view. Recently, novel nonlinear electrical properties of three-terminal ballistic junctions (TBJs) have been discovered theoretically and experimentally. In this work we propose and demonstrate functionality of a novel frequency-doubling device based on a three-terminal ballistic junction. The novel devices are fabricated by integrating a T-shaped TBJ and a one-dimensional (1D) lateral-field-effect transistor (lateral-FET) with trench gate-channel insulation on high-electron-mobility GaInAs/InP quantum well structures The results of the measurements show frequency doubling and gain in these novel devices at room temperature
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| 23. |
- Shorubalko, Ivan, et al.
(författare)
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A novel frequency-multiplication device based on three-terminal ballistic junction
- 2002
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Ingår i: IEEE Electron Device Letters. - 0741-3106. ; 23:7, s. 377-379
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Tidskriftsartikel (refereegranskat)abstract
- In this letter, a novel frequency-multiplication device based on a three-terminal ballistic junction is proposed and demonstrated. A 100 nm-size, three-terminal ballistic junction and a one-dimensional (1-D), lateral-field-effect transistor with trench gate-channel insulation are fabricated from high-electron-mobility GaInAs/InP quantum-well material as a single device. The devices show frequency doubling and gain at room temperature. The performance of these devices up to room temperature originates from the nature of the device functionality and the fact that the three-terminal device extensions are maintained below the carrier mean-free path. Furthermore, it is expected that the device performance can be extended up to THz-range.
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| 24. |
- Shorubalko, Ivan, et al.
(författare)
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Tunable nonlinear current-voltage characteristics of three-terminal ballistic nanojunctions
- 2003
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 83:12, s. 2369-2371
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Tidskriftsartikel (refereegranskat)abstract
- The current-voltage (I-V) characteristics of three-terminal ballistic junctions (TBJs) fabricated from high-electron-mobility GaInAs/InP quantum-well structures are measured in the six-terminal configuration. These characteristics show strong nonlinear, diode-like behavior, in agreement with recent theoretical calculations. Furthermore, the I-V characteristics are tunable by the voltage applied directly to one branch of the TBJs acting as a gate. An additional tuning of the characteristics of the TBJ devices can be performed using an in-plane side gate. All the presented characteristics are measured at room temperature, which makes TBJ devices promising for future nanoelectronic applications. (C) 2003 American Institute of Physics.
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| 25. |
- Wang, SD, et al.
(författare)
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Negative differential capacitance of quantum dots
- 2002
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 65:12
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Tidskriftsartikel (refereegranskat)abstract
- The dependence of charges accumulated on a quantum dot under an external voltage bias is studied. The charge is sensitive to the changes of number of filled levels and the number of conducting levels (channels). We clarify that there are two possible outcomes of applying a bias. (a) The number of conducting channels increases, but the number of filled levels decreases. (b) The number of filled levels increases or does not change while the number of conducting channels (levels) increases with the bias. In case (b), charges are generally expected to increase monotonically with the applied bias. We show, however, that this expectation may not materialize when the electron transmission coefficients depend on bias. Numerical evidences and a theoretical explanation of this negative differential capacitance, i.e., charges accumulated on a quantum dot decrease with applied bias, are presented.
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| 26. |
- Wang, XH, et al.
(författare)
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Decay kinetic properties of atoms in photonic crystals with absolute gaps
- 2003
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Ingår i: Physical Review Letters. - 1079-7114. ; 91:11: 113904
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Tidskriftsartikel (refereegranskat)abstract
- Decay kinetic properties of a two-level atom near the band edges of photonic crystals (PCs) with absolute gaps are studied based on the Green's function expression for the evolution operator. The local coupling strength between the photons and an atom is evaluated by an exact numerical method. It is found that the decay behavior of an excited atom can be fundamentally changed by the variation of the atomic position: Weisskopf-Wigner and non-Weisskopf-Wigner decay phenomena occur at different atomic positions in the PCs as a result of a significant difference in the local coupling strength. Our finding implies that it is possible to engineer the luminescence spectrum by controlling the atomic position.
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| 27. |
- Xu, Hongqi, et al.
(författare)
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A novel device principle for nanoelectronics
- 2002
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Ingår i: Materials Science and Engineering C: Materials for Biological Applications. - 0928-4931. ; 19:1-2, s. 417-420
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Tidskriftsartikel (refereegranskat)abstract
- We report on the results of our recent theoretical and experimental investigations of a novel, room temperature electrical property of three-terminal ballistic junctions (TBJs). For a symmetric TBJ device, it is found that when finite voltages V-1 and V-r are applied in push-pull fashion, with V-1 = V and V-r = - V. to the left and right branches, the voltage output V-c from the central branch will always be negative. This property is in strong contrast to a symmetric three-terminal device made from conventional diffusive conductors, for which Ohm's law predicts a constant zero output of V-c for all V-1 - V-c.This novel characteristic appears even when the device symmetry is broken, provided that V is greater than the threshold. It is also shown that the TBJ devices show a good parabolic behavior for V-c vs. V in a large range of voltages V.
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| 28. |
- Xu, Hongqi
(författare)
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A novel electrical property of three-terminal ballistic junctions and its applications in nanoelectronics
- 2002
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Ingår i: Physica E: Low-Dimensional Systems and Nanostructures. - 1386-9477. ; 13:2-4, s. 942-945
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Tidskriftsartikel (refereegranskat)abstract
- A room-temperature electrical property of three-terminal ballistic junctions (TBJs) is predicted. For a symmetric TBJ. it is shown that when finite voltages F and -V are applied to the left and right branches. the voltage Output V, from the central branch will always be negative. This characteristic appears even when the symmetry in the TBJ is broken. provided that V! is larger than a threshold. Applications of these devices in nanoelectronics are proposed.
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| 29. |
- Xu, Hongqi
(författare)
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Diode and transistor behaviors of three-terminal ballistic junctions
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:5, s. 853-855
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Tidskriftsartikel (refereegranskat)abstract
- We propose new applications of three-terminal ballistic junctions (TBJs) in nanoelectronics. It is found that for a TBJ with one of its three branch contacts, say the right branch contact, being grounded, the output voltage, V-c, from the central branch as a function of the voltage, Vl, applied to the left branch shows a diode characteristic: V-c approximately follows Vl linearly when Vl is negative, and saturates at a small positive value when Vl becomes positive. It is also found that the saturation level of V-c as well as the threshold value of Vl, beyond which V-c saturates, can be modulated by application of a voltage, V-r, to the right branch contact of the TBJ. Thus, the TBJ can also be used as a transistor. TBJ diodes and TBJ transistors with dimensions on the order of sub 100 nm, or much less, can be made from standard high-quality electronic materials with state-of-the-art nanofabrication technology.
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| 30. |
- Xu, Hongqi
(författare)
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Method of calculations for electron transport in multiterminal quantum systems based on real-space lattice models
- 2002
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 66:16
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Tidskriftsartikel (refereegranskat)abstract
- A formalism for the calculations of electron transport in multiterminal quantum systems is presented. The systems are described by tight-binding Hamiltonians. It is shown that by exploiting real-space Green's functions, a problem of the electron transport in a multiterminal system can be reformulated into a problem of the electron transport in an effective two-terminal system and can then be treated using a standard two-terminal method. Applications of the formalism to a three-terminal system, containing a quantum-confined, T-shaped structure, and a four-terminal system, containing a quantum-confined, cross-bar structure, are also presented. It is found that the transmission and reflection probabilities of the two multiterminal quantum systems show complex spectra. The results are explained in terms of the localization properties of the confined states in the systems.
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| 31. |
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| 32. |
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| 33. |
- Xu, Hongqi, et al.
(författare)
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Novel nanoelectronic triodes and logic devices with TBJs
- 2004
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Ingår i: IEEE Electron Device Letters. - 0741-3106. ; 25:4, s. 164-166
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Tidskriftsartikel (refereegranskat)abstract
- In this letter, we demonstrate the realization of novel diodes, triodes, and logic gates with three-terminal ballistic junctions (TBJs) made from a semiconductor heterostructure. The approach exploits the ballistic nature of electron transport, which has emerged in the nanostructures. Importantly, we show that TBJs function as logic AND gates and can be used to construct other compound logic gates, such as NAND gates with voltage gain, when combined with a point contact (an inverter). The demonstrated devices show favorable characteristics such as low turn-on voltage in rectification and room-temperature operation.
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| 34. |
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| 35. |
- Xu, Hongqi, et al.
(författare)
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Reflection phase of scattering electrons in a single-channel atomic wire
- 2003
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 68:24
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical study of the phase property of the reflection coefficient of a single-channel quantum system is presented. This reflection phase information is required for a complete characterization of the scattering problem in the system. It is found that the phase of the reflection coefficient of the system shifts abruptly by pi when the reflection probability passes through a zero. It is also found that in certain systems this phase discontinuity can appear even when no zero and no phase discontinuity are present in the transmission coefficient. Possible experiments for the observation of the reflection phase discontinuity are discussed.
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| 36. |
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| 37. |
- Xu, Hongqi, et al.
(författare)
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Three-terminal ballistic junctions: new building blocks for functional devices in nanoelectronics
- 2002
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Ingår i: 7th International Conference on Nanometer-Scale Science and Technology and 21st European Conference on Surface Science.
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Konferensbidrag (refereegranskat)abstract
- A three-terminal ballistic junction (TBJ) is a device in which three quantum point contacts are coupled via a ballistic region. Previous studies have shown that the TBJs exhibit a novel electrical property which has potential applications in nanoelectronics. Here, based on our recent theoretical and experimental investigations, we will demonstrate that various nanoelectronic devices can be fabricated using the TBJs as building blocks. In particular, the results of our recent design, fabrication, modeling and measurements of TBJ diodes and transistors, TBJ frequency multipliers, and TBJ logic gates will be presented and discussed
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| 38. |
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