| 1. |
- Jeppson, Kjell, 1947, et al.
(författare)
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Theory of a room-temperature silicon quantum dot device as a sensitive electrometer
- 2004
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Ingår i: Journal of Applied Physics. - Melville, NY : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 95:1, s. 323-326
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Tidskriftsartikel (refereegranskat)abstract
- We consider theoretically the use of a room-temperature silicon quantum dot based device for electrometer applications. The low power device includes two split gates that quantize the electronic energy levels in the emitter and collector regions. The base consists of a silicon quantum dot buried in silicon dioxide. The small size of the dotand quantization of the states in the leads combined to allow the device to operate at room temperature. The nonlinear current-voltage characteristics can be significantly altered by small changes to the potential of the split gates. Power dissipation in the device therefore changes with the split gate voltage, and this can be exploited in electrometerapplications. A simple model of the power dissipated when the device is part of a microwave resonant inductor-resistor-capacitor tank circuit suggests that large changes indevice power can be achieved by changing the gate voltage, thereby forming a measurable signal. We also demonstrate that the power dissipation in the device changes as the base width is varied, and that the current through the device increases exponentially with a decrease in base width. (©2004 American Institute of Physics)
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| 2. |
- Narayan, V., et al.
(författare)
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Calculation of the temperature dependence of hot electron scattering in heavily p-doped GaAs using a high-temperature approximation to the dielectric function
- 2002
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 324:1-4, s. 393-402
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Tidskriftsartikel (refereegranskat)abstract
- Using a high-temperature approximation to the dielectric function within the random phase approximation, we calculate hot electron scattering rates, as a function of temperature and doping density, in p-doped GaAs. The dielectric function of the holes contains contributions from intraband excitations and interband excitations. The former reduces to an analytic form within the two pole approximation (which used Boltzmann statistics), whereas the latter was calculated numerically. The collective excitation mode of the holes was defined by intraband excitations, since at very small wavevectors, the interband excitations vanish. However, at low temperature the interband excitations were found to be the dominant Landau damping mechanism, which strongly suppressed the plasmon at moderate doping levels. At high temperature the excitations from the heavy to light band were partially suppressed, and the plasmon was not overwhelmingly Landau damped by either interband or intraband excitations. At room temperature, an analytic dielectric function where the interband excitations have been neglected, may be used to accurately calculate hot electron mean free paths. This approximation was found to become more accurate with lower doping levels, but was not appropriate at low temperature. © 2002 Elsevier Science B.V. All rights reserved.
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| 3. |
- Narayan, V, et al.
(författare)
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Monte Carlo simulation of controlled impurity diffusion in semiconductors using split gates
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 65:7
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Tidskriftsartikel (refereegranskat)abstract
- We propose an experiment, where impurity diffusion in a semiconductor layer during heat treatment, can be controlled by a nonlinear potential produced by split gates. We approximated the nonlinear potential as a parabola centered at the middle of the semiconductor layer; the impurities diffuse into the central region. Starting with the phenomenological Arrhenius equation, we describe a simple model for the impurity diffusion, and then perform Monte Carlo simulations to predict the impurity profile, for different parabolic constants and impurity densities. The results show that charge builds up in the central area creating a long-range internal electric field. The internal field at high doping levels. can be of sufficient strength to cause the broadening of the impurity density profile. The width of the impurity profile can be controlled by the curvature of the parabola, which in turn depends on the split-gate geometry and voltage.
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| 4. |
- Narayan, V, et al.
(författare)
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Proposed experiments to grow nanoscale p-n junctions and modulation-doped quantum wires and dots
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 65:12
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Tidskriftsartikel (refereegranskat)abstract
- We propose and model several experiments where the field effect defined by split gates is used to restrict acceptors and donors to regions of a semiconductor layer. The nonlinear potential defined by split gates restricts positive donors to the center of the layer, whereas the negative acceptors localize near the edges. The Arrhenius equation modified to include effects of the external and internal fields is used to calculate time- and position-dependent impurity hopping probabilities for Monte Carlo simulations of the experiments. The results show that at high doping levels, the internal field resists high concentrations of net charge, and "flattens" the doping profile. In addition, we perform Monte Carlo simulations, where the split gates move relative to the semiconductor sample, to demonstrate how regions of a semiconductor layer can be cleared of unwanted impurities. Finally, we discuss how a "chessboard" arrangement of square gates can be employed to create modulation-doped quantum dot arrays.
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| 5. |
- Narayan, V, et al.
(författare)
-
Split gate nanoscale Coulomb driven stochastic resonance mechanism for separating like-charged impurities in semiconductors
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 69:7
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Tidskriftsartikel (refereegranskat)abstract
- A proposed experiment is modeled using a Monte Carlo simulation. In the simulation split gates define a nonlinear flashing potential within a semiconductor layer that contains two species of like-charged impurities with different mobilities. Flashing the external potential purifies the split gate region of the more mobile species, since impurities that have escaped are effectively unable to re-enter the split gate region. The model takes into account the Coulomb repulsion between the impurities. We demonstrate that the segregation efficiency and the purification rate are sensitive to the impurity density and strength of the confining potential, since Coulomb interaction aids the purification rate and also increases the unwanted leakage of the less mobile species.
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| 6. |
- Sundqvist, P A, et al.
(författare)
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Spherical quantum dot with added parabolic confinement as a nanoscale tunable radiation detector
- 2002
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier Science B.V., Amsterdam.. - 1386-9477 .- 1873-1759. ; 15:1, s. 27-32
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Tidskriftsartikel (refereegranskat)abstract
- We have calculated the optical absorption matrix elements for a spherical silicon quantum dot embedded in silicon dioxide with the addition of a parabolic potential which is used to tune the bound state energy levels. The photon absorption from the ground state to the excited states was calculated as a function of the parabolic potential curvature constant and the dot radius which varied between 2 and 6 nm. The results show that we can tune the wavelength in the entire visible range. Furthermore, the absorption cross section was found to change by several orders of magnitude with increasing parabolic potential curvature constant. For large parabolic curvature constant the transition move out of the visible range, and the number of allowed transition increased with the dot radius.
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| 7. |
- Sundqvist, PA, et al.
(författare)
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Electronic subbands of Monte Carlo simulated doping profiles defined by a split gate potential during thermal treatment
- 2003
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Ingår i: Journal of Applied Physics. - : American Institute of Physics. - 0021-8979 .- 1089-7550. ; 93:5, s. 2712-2718
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Tidskriftsartikel (refereegranskat)abstract
- We studied a model in which an external one-dimensional parabolic potential defined by split gates is used during heat treatment to calculate impurity profiles with an approximately Gaussian distribution in a semiconductor layer. Using a recently published model, the impurities are moved by a Monte Carlo procedure, to calculate equilibrium impurity profiles for different layer thicknesses and initial doping levels. The samples are cooled and the electronic subbands are then calculated self-consistently by coupling the Schrodinger equation with a charge neutral Poisson equation for temperatures between 40-300 K. The model includes temperature and doping concentration dependent impurity ionization rates. The polarity and strength of the split gate voltage may be altered to affect the subband energies and wave functions. When a parabolic potential with a negative constant was added, we found that it is possible to produce a charge density that consists of two peaks located near the quantum well walls. This effect is slightly washed out at room temperature. For a parabolic potential with a large and positive constant, the charge density becomes sharply localized at the middle of the quantum well. Throughout the calculations, we have used slightly nonsymmetric doping profiles.
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| 8. |
- Sundqvist, PA, et al.
(författare)
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Self-consistent drift-diffusion model of nanoscale impurity profiles in semiconductor layers, quantum wires, and quantum dots
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:16
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Tidskriftsartikel (refereegranskat)abstract
- We propose and model an experiment where impurity profiles in low dimensional structures can be controlled (during heat treatment) by an external parabolic potential defined by a variety of gate arrangements. At high temperatures the impurities are ionized and are able to move relatively quickly. After a realistic equilibrium time of typically one hour, the profiles are rapidly cooled such that the impurities are frozen in place. The model, which takes the electronic distribution as well as the mobile impurities into account results in a nonlinear Poisson equation. Similar models are widely used in semiconductor device theory where doping profiles are fixed. A parabolic potential in one, two, and three dimensions is applied to a semiconductor layer, a cylindrical quantum wire, and a spherical quantum dot, respectively. The impurity profiles are typically Gaussian shaped, where the distribution broadens with increasing temperature. The results demonstrate that the profile can be widely altered by changing the temperature, the average doping density, the size (radius), and the parabolic potential constant. The effect of parabolic confinement dimensionality on the diffusion is also studied. The temperature effect is studied up to a theoretical zero-temperature limit for which an analytic solution for the impurity profile is derived. The impurity profiles are sharper as the parabolic constant increases and the processing temperature is lowered. The processing time, however, increases exponentially as the temperature is lowered, and this must be considered in the practical situation.
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| 9. |
- Vincent, Jonathan, et al.
(författare)
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Theory of a room-temperature silicon quantum dot transitor as a sensitive electrometer
- 2004
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 95, s. 323-
-
Tidskriftsartikel (refereegranskat)abstract
- We consider theoretically the use of a room-temperature silicon quantum dot based device for electrometer applications. The low power device includes two split gates that quantize the electronic energy levels in the emitter and collector regions. The base consists of a silicon quantum dot buried in silicon dioxide. The small size of the dot and quantization of the states in the leads combined to allow the device to operate at room temperature. The nonlinear current–voltage characteristics can be significantly altered by small changes to the potential of the split gates. Power dissipation in the device therefore changes with the split gate voltage, and this can be exploited in electrometer applications. A simple model of the power dissipated when the device is part of a microwave resonant inductor-resistor-capacitor tank circuit suggests that large changes in device power can be achieved by changing the gate voltage, thereby forming a measurable signal. We also demonstrate that the power dissipation in the device changes as the base width is varied, and that the current through the device increases exponentially with a decrease in base width.
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| 10. |
- Vincent, JK, et al.
(författare)
-
Tuning the room temperature nonlinear I-V characteristics of a single-electron silicon quantum dot transistor by split gates: A simple model
- 2002
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 65:12
-
Tidskriftsartikel (refereegranskat)abstract
- We propose an experiment that potentially allows a single-electron silicon quantum dot transistor to operate at room temperature. The emitter and collector of the device consist of silicon quantum wires and the base contains a single silicon dot buried in silicon dioxide. We suggest that split gates are added to the usual experimental situation, to provide additional and variable confinement perpendicular to the transport direction in the emitter and collector regions. The current-voltage curve is calculated using the Bardeen transfer Hamiltonian method. The potential defined by the gates is approximated to a harmonic form. We predict the nonlinear structure in the current-voltage curve, will survive to room temperature for systems with an emitter and collector with dimensions of the order 20-40 nm, and where the harmonic potentials have subband level spacing of the order 4-8.5 meV. Furthermore, we predict that the peak positions and peak to valley ratios in the current-voltage curve can be "tuned" by changing the split gate voltage.
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