Modeling of transport behavior of the ballistic Silicon nanowire gate-all-around field-effect-transistors (Si NWFETs) with Si/SiO 2 interface roughness
01 Dec 2012-pp 1-4
TL;DR: In this article, the contribution of gate oxide/channel interface roughness has been estimated and incorporated into the transport models of a Si nanowire field effect transistor (Si NWFET) by modifying the relevant energy subbands taking into account the roughness in both transverse and longitudinal directions.
Abstract: In the current work, the contribution of gate oxide/channel interface roughness has been estimated and incorporated into the transport models of a Si nanowire field-effect-transistor (Si NWFET). This has been incorporated by modifying the relevant energy sub-bands taking into account the roughness in both transverse and longitudinal directions. Accordingly, the channel Hamiltonian matrix elements related to energy sub-bands are modified. It has been observed from the study that such interface roughness has significant effect on the device performance in terms of transfer and output characteristics. The transfer characteristics show that the current decreases up to 40% for an increase in interface roughness up to 25%.
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TL;DR: It is found that for donors and acceptors, the DFT charge distribution extends similarly in both materials, and the relaxed structure produces a 50% larger spread of electronic charge as compared with unrelaxed Si and GaAs.
Abstract: In this work, electron densities around dopants in Si and GaAs have been calculated using density functional theory (DFT) calculations. These extracted densities have been used to describe dopants in an in-house non-equilibrium Green functions device simulator. The transfer characteristics of nanowire gate all around field effect transistor have been calculated using DFT electron densities. These transport calculations were compared with those using a point charge model of the dopant. The dopants are located in the middle of the channel of the device. Specifically, DFT calculations of a 512 atom Si supercell with a single impurity atom have been carried out, both phosphorous and boron atoms have been used as donor and acceptor impurities respectively. The calculations were repeated on a gallium arsenide supercell, where the silicon atom substituted gallium and arsenide to act as donor and acceptor respectively. We found that for donors and acceptors, the DFT charge distribution extends similarly in both materials. In addition, the relaxed structure produces a 50% larger spread of electronic charge as compared with unrelaxed Si and GaAs. The extracted current voltage characteristics of the devices are altered significantly using the charge density obtained by DFT. At 0.7 V the current in Si is 20% larger using the DFT charge density compared to the point charge model for donors. Whereas the current using the point charge model in GaAs is 2.5 times larger than the distributed charge. Devices exhibit substantial tunnelling currents for donors and acceptors irrespective of the model of the dopant considered. In GaAs, this was 76% using a point charge and 78% using the distributed charge when using a donor; 61% and 68% in Si respectively. The tunnelling current using acceptors for Si was 100% and 99% using GaAs for both models.
2 citations
Cites background from "Modeling of transport behavior of t..."
...As a result, silicon (Si) nanowire field effect transistors (NWFETs) have been in production for several years and exhibit superior performance for low power devices and fast switching [1, 2]....
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Journal Article•
1 citations
20 Apr 2023
TL;DR: In this paper , a dual-gate GaAs nanowire FET with state-of-the-art miniaturized dimensions for high performance charge qubit operation at room temperature is considered.
Abstract: The current work explores a geometrically engineered dual gate GaAs nanowire FET with state of the art miniaturized dimensions for high performance charge qubit operation at room temperature. Relevant gate voltages in such device can create two voltage tunable quantum dots (VTQDs) underneath the gates, as well as can manipulate their eigenstate detuning and the inter-dot coupling to generate superposition, whereas a small drain bias may cause its collapse leading to qubit read out. Such qubit operations, i.e., Initialization, Manipulation, and Measurement, are theoretically modeled in the present work by developing a second quantization filed operator based Schrodinger-Poisson self-consistent framework coupled to non-equilibrium Greens function formalism. The study shows that the Bloch sphere coverage can be discretized along polar and azimuthal directions by reducing the nanowire diameter and increasing the inter-dot separation respectively, that can be utilized for selective information encoding. The theoretically obtained stability diagrams suggest that downscaled nanowire diameter and increased gate separation sharpen the bonding and anti-bonding states with reduced anticrossing leading to a gradual transformation of the hyperbolic current mapping into a pair of straight lines. However, the dephasing time in the proposed GaAs VTQD-based qubit may be significantly improved by scaling down both the nanowire diameter and gate separation. Therefore, the present study suggests an optimization window for geometrical engineering of a dual gate nanowire FET qubit to achieve superior qubit performance. Most importantly, such device is compatible with the mainstream CMOS technology and can be utilized for large scale implementation by little modification of the state of the art fabrication processes.
References
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TL;DR: The non-equilibrium Green's function (NEGF) formalism provides a sound conceptual basis for the devlopment of atomic-level quantum mechanical simulators that will be needed for nanoscale devices of the future as discussed by the authors.
1,094 citations
"Modeling of transport behavior of t..." refers background in this paper
...Initially a Si nanowire channel with perfectly smooth Si/SiO2 interface is represented by a Hamiltonian with open boundary conditions at the source and drain contacts [7]....
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TL;DR: In this article, the electronic transport properties of nanowire field effect transistors (NW-FETs) are discussed in detail, and four different device concepts are studied in detail.
Abstract: This paper discusses the electronic transport properties of nanowire field-effect transistors (NW-FETs). Four different device concepts are studied in detail: Schottky-barrier NW-FETs with metallic source and drain contacts, conventional-type NW-FETs with doped NW segments as source and drain electrodes, and, finally, two new concepts that enable steep turn-on characteristics, namely, NW impact ionization FETs and tunnel NW-FETs. As it turns out, NW-FETs are, to a large extent, determined by the device geometry, the dimensionality of the electronic transport, and the way of making contacts to the NW. Analytical as well as simulation results are compared with experimental data to explain the various factors impacting the electronic transport in NW-FETs.
352 citations
"Modeling of transport behavior of t..." refers background in this paper
...As a result, the gate all-around silicon (Si) nanowire-FETs (Si-NWFETs) have been emerged as one of the potential alternatives for advanced highperformance low-power nanoelectronic devices and switches [1]....
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...INTRODUCTION The gradual down-scaling of metal-oxide-semiconductor field-effect-transistors (MOSFETs) for successive performance improvement has been limited by the deleterious short channel effects and poor electrostatic control on its channel either through single, double or tripple gate [1]....
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TL;DR: In this article, a 3D quantum simulator for the silicon nanowire transistor (SNWT) is presented, where the authors use Buttiker probes to simulate the effects of scattering on both internal device characteristics and terminal currents.
Abstract: The silicon nanowire transistor (SNWT) is a promising device structure for future integrated circuits, and simulations will be important for understanding its device physics and assessing its ultimate performance limits. In this work, we present a three-dimensional (3D) quantum mechanical simulation approach to treat various SNWTs within the effective-mass approximation. We begin by assuming ballistic transport, which gives the upper performance limit of the devices. The use of a mode space approach (either coupled or uncoupled) produces high computational efficiency that makes our 3D quantum simulator practical for extensive device simulation and design. Scattering in SNWTs is then treated by a simple model that uses so-called Buttiker probes, which was previously used in metal-oxide-semiconductor field effect transistor simulations. Using this simple approach, the effects of scattering on both internal device characteristics and terminal currents can be examined, which enables our simulator to be used f...
351 citations
TL;DR: In this paper, a 3D quantum simulator for the silicon nanowire transistor (SNWT) is presented, where the authors use Buttiker probes to simulate the effects of scattering on both internal device characteristics and terminal currents.
Abstract: The silicon nanowire transistor (SNWT) is a promising device structure for future integrated circuits, and simulations will be important for understanding its device physics and assessing its ultimate performance limits. In this work, we present a three-dimensional quantum mechanical simulation approach to treat various SNWTs within the effective-mass approximation. We begin by assuming ballistic transport, which gives the upper performance limit of the devices. The use of a mode space approach (either coupled or uncoupled) produces high computational efficiency that makes our 3D quantum simulator practical for extensive device simulation and design. Scattering in SNWTs is then treated by a simple model that uses so-called Buttiker probes, which was previously used in metal-oxide-semiconductor field effect transistor (MOSFET) simulations. Using this simple approach, the effects of scattering on both internal device characteristics and terminal currents can be examined, which enables our simulator to be used for the exploration of realistic performance limits of SNWTs.
326 citations
"Modeling of transport behavior of t..." refers methods in this paper
...The Hamiltonian is solved by non-equilibrium Green’s function (NEGF) method to obtain the transmission coefficient ( D S T → ) [9]....
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TL;DR: In this article, a 10-band sp3d5s* semi-empirical atomistic tight-binding model coupled to a self-consistent Poisson solver is used for the dispersion calculation.
Abstract: Bandstructure effects in the electronic transport of strongly quantized silicon nanowire field-effect-transistors (FET) in various transport orientations are examined. A 10-band sp3d5s* semiempirical atomistic tight-binding model coupled to a self-consistent Poisson solver is used for the dispersion calculation. A semi-classical, ballistic FET model is used to evaluate the current-voltage characteristics. It is found that the total gate capacitance is degraded from the oxide capacitance value by 30% for wires in all the considered transport orientations ([100], [110], [111]). Different wire directions primarily influence the carrier velocities, which mainly determine the relative performance differences, while the total charge difference is weakly affected. The velocities depend on the effective mass and degeneracy of the dispersions. The [110] and secondly the [100] oriented 3 nm thick nanowires examined, indicate the best ON-current performance compared to [111] wires. The dispersion features are strong functions of quantization. Effects such as valley splitting can lift the degeneracies particularly for wires with cross section sides below 3 nm. The effective masses also change significantly with quantization, and change differently for different transport orientations. For the cases of [100] and [111] wires the masses increase with quantization, however, in the [110] case, the mass decreases. The mass variations can be explained from the non-parabolicities and anisotropies that reside in the first Brillouin zone of silicon.
192 citations
"Modeling of transport behavior of t..." refers background in this paper
...The corresponding electron effective mass components are taken from [10]....
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