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ABSTRACT: A flow of independent particles, traveling across a biased heterostructure, is shown to produce an essentially constant probability current density in the gate. Based on this observation, a phenomenological boundary condition was proposed for evaluating the eigenfunctions of the Hamiltonian and for the computing the gate probability current density in a three-layer metal-oxide-semiconductor (MOS) heterostructure. Sharp antiresonances are obtained in the probability current, which are interpreted as quasi-bound states in the heterostructure. Results show that the antiresonant states should contribute the least to the gate current as the particles are strongly localized behind the interfacial barrier. The main contribution to the gate current of the MOS structure should come from the states between the antiresonances which are always supplied with particles from the bulk.
Journal of Nanoscience and Nanotechnology 03/2009; 9(2):1237-41. · 1.56 Impact Factor
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ABSTRACT: The paper presents models and computations for neutralization of space charge effects using electrons provided by field emitter arrays. Different ion species (11B+,31P+,75As+) with energy in the range Eion = 200 eV‐1 keV have been considered. The ion beam divergence is studied as a function of electron beam geometry and physical parameters (electron and ion energy, electron∕ion current ratio Iel/Iion). The electron beam geometry takes into account electron source positions and initial launching angles. It is shown that optimal ion beam neutralization occurs for low energy electrons emitted parallel to the ion beam.
AIP Conference Proceedings. 11/2008; 1066(1):265-268.
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ABSTRACT: A linear array of gated carbon nanotubes (CNTs) is proposed for improving the array electron emission properties by controlling the electric field conversion factor and its uniformity. The CNT emission current has been computed according to a previously developed model that takes into account the low dimensionality of the CNT electronic system. The CNT field conversion factor (for single CNT and linear array gated CNTs) has been numerically derived using the OPERA3D/TOSCA software and then expressed analytically. For better performance, controlling the parallelism of the CNTs in the array is not a strong requirement, but controlling their height is. The position of the CNT array emission current optimum depends on the value of parameters chosen, but generally it is obtained for array packing density ratio a/h<sub>n</sub> (array pitch/CNT height) taking value in the range of 0.5–1.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 04/2008; · 1.34 Impact Factor
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ABSTRACT: In the present paper, we present an electroluminescence (EL) model for a tunneling carrier injection light-emitting diode based on insulator-embedded Si-nc.
Vacuum Nanoelectronics Conference, 2007. IVNC. IEEE 20th International; 08/2007
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ABSTRACT: Linear (or quasi-linear, such as spiral shaped) CNT arrays exhibit improved electron emission performance as compared to two-dimensional arrays. Modeling results show that the field uniformity within the CNT array is an important factor for achieving improved electron emission properties. Optimized linear CNTs films may be used to realize high performance nanotriodes or electron sources.
Vacuum Nanoelectronics Conference, 2007. IVNC. IEEE 20th International; 08/2007
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ABSTRACT: In the present work, we consider a system of a grounded CNT of length L and radius r<sub>0</sub> (the emitter) facing a spherical anode of radius R<sub>a</sub>(R<sub>a</sub>>>r<sub>0</sub>). The anode is placed at some distance away from the emitter's tip. The CNT is modelled as a two-dimensional (2D) manifold where electrons behave as quasi-free and independent particle. The electrons are bound on the CNT surface by a one-dimensional (1D) potential well, due to the restriction imposed by the cylindrical symmetry. In order to have a full description of the electron behaviour in the whole system, a potential energy in the vacuum region needs also to be defined. To this purpose, the CNT cap is simplified as a grounded conducting sphere of radius r<sub>0</sub> facing the anode on the same symmetry axis. As the emitter-anode distance, d and the anode radius, R<sub>a</sub> are much greater than r<sub>0</sub>, the electric field in vacuum may be computed using the method of electrostatic images.
Vacuum Nanoelectronics Conference, 2007. IVNC. IEEE 20th International; 08/2007
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ABSTRACT: Computations for three-dimensional diode/triode configurations involving regular arrays of carbon nanotubes (CNTs) have been performed. The numerical results have been used to derive analytical relationships for the CNT electric field. These relationships, together with a previously obtained analytical formula giving the CNT electron emission current, allow the computation of the array current as function of various parameters. For diode configurations, an optimum spacing of the CNT array is shown to exist. Triode configurations with regular CNT arrays have highly nonuniform fields, the CNTs placed at the array edge providing more than 90% of the array current.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 04/2007; · 1.34 Impact Factor
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ABSTRACT: The tunneling of electrons through metal–oxide–silicon (MOS) structures with ultra-thin oxide is modeled using a linear model for the electron potential energy, an approach which simplifies the computation of both the interface potential and the field penetration distance in the substrate. The one-particle quantum problem is split into finding the metastable states induced by the internal field penetration in the substrate and the running states in the gate region. The two states are assumed to be connected by the condition for the continuity of the probability density at the substrate–dielectric interface. The electron probability current and the total gate current density are obtained for different gate voltages. As the model yields excellent fittings with experimental current–voltage (I–V) data for MOS structures, it was further applied to constant current stressing analysis in order to obtain values for important electron trapping parameters in the oxide. The resultant estimates of the electron trapping cross-section fall in the range of other independent determinations in the literature.
Microelectronics Reliability. 01/2006;
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ABSTRACT: In this paper, using a continuum two-dimensional model, the dependence on the carbon nanotube (CNT) size for the quasi-free electrons distribution on the CNT surface is derived.
Vacuum Nanoelectronics Conference, 2005. IVNC 2005. Technical Digest of the 18th International; 08/2005
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ABSTRACT: This paper reports characterization results for the field emission statistics of the HfC/poly-Si arrays. A model for the array field emission has been developed, considering non-uniform distributions for both the radius and the work function. Array current-voltage measurements were used to extract model parameters.
Vacuum Nanoelectronics Conference, 2005. IVNC 2005. Technical Digest of the 18th International; 08/2005
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ABSTRACT: This paper presents two models for application in multilayer electron sources. In both models the substrate is a semiconductor and the source of the field-emitted electrons generated is in the accumulation layer generated at the silicon-wide band gap material(WBG) interface by the penetration of the intense extraction field. In the "coherent approach", quantum connections between the envelopes of electron wave functions in each region of the structure are taken into account. However, in order to comply with the difference between the probability current in the vacuum and in the substrate, a relaxed connection condition is accepted at the semiconductor-WBG interface. This results in the emission current exhibiting some resonant maxima in the current-electric field plots. In the alternative approach, a sequential tunneling is allowed between the substrate and the vacuum regions, with temporary accumulation of electrons in the conduction band of the WBG material. The increase of space charge in the WBG produces an overall decrease in the internal field in the first barrier and thus reduces the electron injection from the substrate. An optimum height of the vacuum chamber with corresponding maximum field emission current is obtained due to the two concurrent effects of lowering the injection barrier and increasing the amount of space charges.
Vacuum Nanoelectronics Conference, 2005. IVNC 2005. Technical Digest of the 18th International; 08/2005
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ABSTRACT: A model for electron field emission from carbon nanotubes (CNTs) has been developed and modeling results are presented. The model assumes that for high emission currents, part of the electrons behave as quasifree. As a result, the spatial confinement quantization of their states appears, the tunneling field emission taking place from these states into the vacuum. The probability of finding an electron in a small axial interval is higher close to the CNT cylindrical body, while the extraction field is higher on the CNT hemispherical tip. These two opposite trends lead to enhancement of the CNT lateral field emission for higher extraction voltages. The model outlines the possibility of-inhomogeneous electron field emission for very thin CNTs at high emission levels and the appearance of peculiar ring-shaped and/or spot-shaped field emission images, in accordance to available experimental observations. (c) 2005 American Vacuum Society.
Journal of Vacuum Science and Technology B. 01/2005; 23(2):649-656.
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ABSTRACT: A model of coherent electron field emission from a semiconductor substrate through a very thin (nanometer-wide) dielectric layer is developed. The model includes a separate approach for the electron transmission from the bulk, substrate conduction band and from the quasi-bound states induced by the applied field at the substrate-dielectric boundary. No artificial quantization condition is used for the energies of the quasi-bound states. "Resonant" behavior is found in the total emission current density, which may give rise to consistent enhancement as compared to the emission from bare substrate surface, in accordance with other results in the literature.
Semiconductor Conference, 2004. CAS 2004 Proceedings. 2004 International; 11/2004
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ABSTRACT: In this paper, the role of the semiconductor interface layer electrons in the field emission current is discussed by considering a simplified model of the semiconductor and vacuum interfaces. Also, the extent to which the quasi-bound states are populated during the field emission process is outlined in this study.
Vacuum Nanoelectronics Conference, 2004. IVNC 2004. Technical Digest of the 17th International; 08/2004
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ABSTRACT: Test arrays of gated Si emitters with N<sub>tips</sub>=100 tips have been fabricated. A HfC coating layer was deposited on the tips, showing effectiveness in lowering the operational voltage and improving the uniformity of the array emission. The Si and Si/HfC emitter arrays were measured in high vacuum conditions and after being subject to Ar and O<sub>2</sub> residual gases with partial pressures in the range 10<sup>-4</sup> to 10<sup>-6</sup> Pa, the evolution in time of the emission properties being recorded. The influence of residual gases on the field emission (FE) properties has been comparatively characterized through model parameter extraction.
Vacuum Nanoelectronics Conference, 2004. IVNC 2004. Technical Digest of the 17th International; 08/2004
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ABSTRACT: Ring-shaped images may appear under high field emission conditions for very thin carbon nanotubes (CNTs). Such image patterns cannot be explained by the corresponding field enhancement only. A model for electron field emission from the CNT is developed. The model refers to a capped nanotube (with cylindrical body and hemispherical cap). It is assumed that for high emission currents/high local temperatures, part of the electrons behave as quasi-free. As a result, the spatial confinement quantization of their states appears. The Schrodinger equation for the single electron can be solved separately on the cylindrical and spherical parts of the structure and the corresponding solutions can be connected smoothly at the circular intersection of the two regions. Many electronic states that are possible on the two regions separately turn out to be forbidden for the capped nanotube. The selection of the possible electronic states under the aforementioned complex conditions is determined by the geometric parameters of the tube, namely the ratio between its length and diameter. The occupation of the allowed one- electron states is considered as governed by the usual Fermi statistics. Together with the quantum probability of finding an electron in some specified area of the surface, this gives the electron distribution on the tube, which is one of the key factors determining the electron field emission from the CNT. Another key factor is the applied extraction field. The extraction field has been numerically computed using Simion nanotube-on-post diode configuration.
Vacuum Nanoelectronics Conference, 2004. IVNC 2004. Technical Digest of the 17th International; 08/2004
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ABSTRACT: Films of vertically aligned carbon nanotubes (CNTs) have recently being grown within patterned areas. Nanotriodes based on such CNT arrays as field emitters have the potential of improved performance if devising a way to subject the nanotubes to uniform extraction fields. In this paper, we propose and model an optimized nanotriode with CNTs of variable heights. The bunch of variable-height CNTs is centrally placed in the opening of the gate electrode, the CNTs being taller in the middle and shorter toward the bunch edge. An analytical model to describe the electric field distribution is derived. The nanotriode characteristics have been calculated as function of the device geometry and its functional parameters. Optimal nanotriode configurations assuring quasi-uniform extraction fields and enhanced emission currents have been shown to exist.
Electron Devices and Solid-State Circuits, 2003 IEEE Conference on; 01/2004
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ABSTRACT: Vertically aligned carbon nanotubes (CNTs) grown in patterned areas are used as electron sources in field emission displays (FEDs), but detrimental electron beam spreading may occur in a vacuum space. In this paper, a novel emitter structure with two coaxial electrodes and vertically aligned CNTs is proposed and analyzed using three-dimensional (313) computation of the electric field. One of the gate electrodes plays a role in electron extraction and the other one in electron beam focusing. Unlike the case of double-gated Spindt emitters, the focusing gate electrode is placed near the plane of the CNT tips while the extraction electrode is placed at some distance from it. An improved electric field uniformity within the CNT array and focusing of the electron beam are thus achieved. Electron beam confinement characteristics and field emission properties are calculated as functions of device geometry and its functional parameters.
Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes & Review Papers. 01/2004; 43(6A):3328-3334.
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ABSTRACT: Films of vertically aligned carbon nanotubes (CNTs) have recently being grown within patterned areas. Nanotriodes based on such CNT arrays as field emitters have the potential of improved performance if devising a way to subject the nanotubes to uniform extraction fields. In this paper, we propose and model an optimized field emission nanotriode with aligned CNTs of variable heights. The bunch of variable-height CNTs is centrally placed in the opening of the gate electrode, the CNTs being taller in the middle and shorter toward the bunch edge. A proof-of-concept analytical model to describe the electric field distribution is derived. Numerical computations of the electric field for three-dimensional structural configurations taking into account the CNT reciprocal field screening have been performed. The nanotriode characteristics have been calculated as a function of device geometry and its functional parameters. Optimal nanotriode configurations assuring quasi-uniform extraction fields and enhanced emission currents have been shown to exist.
Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes & Review Papers. 01/2004; 43(2):485-491.
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ABSTRACT: In this paper, we propose a model of spatial confinement quantization of electron states and of tunneling field emission from these states. The model can also account for the observed orders-of-magnitude differences between the total emission currents from capped and opened CNT, even if one neglects the edge-induced field enhancement at opened CNT tips.
Vacuum Microelectronics Conference, 2003. Technical Digest of the 16th International; 08/2003
