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Non-Equilibrium Green's Function based Circuit Models for Coherent Spin Devices
摘要： With recent developments in spintronics, it is now possible to envision 'spin-driven' devices with magnets and interconnects that require a new class of transport models using generalized Fermi functions and currents, each with four components: one for charge and three for spin. The corresponding impedance elements are not pure numbers but 4 × 4 matrices. Starting from the Non-Equilibrium Green's Function (NEGF) formalism in the elastic, phase-coherent transport regime, we develop spin generalized Landauer-Büttiker formulas involving such 4 × 4 conductances, for multi-terminal devices in the presence of Normal-Metal (NM) leads. In addition to usual 'terminal' conductances describing currents at the contacts, we provide 'spin-transfer torque' conductances describing the spin currents absorbed by ferromagnetic (FM) regions inside the conductor, specifying both of these currents in terms of Fermi functions at the terminals. We derive universal sum rules and reciprocity relations that would be obeyed by such matrix conductances. Finally, we apply our formulation to two example Hamiltonians describing the Rashba and the Hanle effect in 2D. Our results allows the use of pure quantum transport models as building blocks in constructing circuit models for complex spintronic and nano-magnetic structures and devices for simulation in SPICE-like simulators.
关键词： Rashba effect,spintronics,Landauer-Büttiker formula,spin-transfer torque,Non-Equilibrium Green's Function,Hanle effect,SPICE simulation
更新于2025-09-23 15:23:52
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Transport properties of doped zigzag graphene nanoribbons
摘要： Numerous studies on materials have driven the development of modern nanoelectronic devices. And research also shown that the integrated circuits have entered the era of the nanoelectronic scales from the scale of microelectronics. But the limitations of copper as a traditional connection, such as the resistivity increases a lot, further causing a lot of heat in the interconnect, have been highlighted. Therefore, we need new materials as the substitution of copper. The metallic properties exhibited by the zigzag graphene nanoribbons (ZGNRs) can be controlled by the edge states, doping and different widths of the nanoribbons. In this paper, we applied simulation to dope copper atom chains on ZGNRs. We found an energetic phenomenon that after doping the nanoribbons conductivity have increased significantly than the original. In addition, the transmission channels are mainly concentrated near the doping position, and the width used for transmission is greatly reduced after doping. It is expected to be used as an inter-connect application in nano-integrated circuits in the future.
关键词： Density functional theory,Interconnect,Electronic transport property,Non-equilibrium Green's function,Zigzag graphene nanoribbons,Doping
更新于2025-09-23 15:23:52
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[IEEE 2018 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) - Austin, TX, USA (2018.9.24-2018.9.26)] 2018 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) - The Impact of Dopant Diffusion on Random Dopant Fluctuation in Si Nanowire FETs: A Quantum Transport Study
摘要： In this work, we perform statistical quantum transport simulations with 3×3 nm2 Si nanowire (NW) field-effect transistors (FETs) to investigate the impact of dopant diffusion on random dopant fluctuation. First, we use an effective mass Hamiltonian for the transport where the confinement and transport effective masses are extracted from the tight-binding band structure calculations. The dopant diffusion along the transport direction from the source/drain regions to the channel region is modeled by the Gaussian doping profile. To generate random discrete dopants, we adopt a rejection scheme considering the 3-dimensional atomic arrangement of the NW structures. Our statistical simulation results show that the diffused dopants into the channel region cause large variability problems in Si NW FETs.
关键词： non-equilibrium Green's function,tight-binding,dopant diffusion,random discrete dopants,silicon nanowire
更新于2025-09-23 15:22:29
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Superior Sensing Properties of Black Phosphorus as Gas Sensors: A Case Study on the Volatile Organic Compounds
摘要： The unique structure and prominent properties of black phosphorus (BP) and its monolayer and multilayers in device applications have attracted significant attention to this elemental 2D material. In this study, a comprehensive evaluation of the candidacy of monolayer BP as a channel material for high-performance volatile organic compound (VOC) sensors is conducted combining first-principles density functional theory calculations and non-equilibrium Green’s function formalism. The adsorption configurations and energetics of several typical VOCs (ethanol, propionaldehyde, acetone, toluene, and hexane) on monolayer BP are examined and it is demonstrated that VOCs generally exhibit stronger interaction with monolayer BP than with the widely studied monolayer MoS2, indicative of monolayer BP potentially being a more sensitive VOC sensor. Monolayer BP is shown to exhibit highly anisotropic transport behaviors, whereas the absolute modification of current–voltage responses due to VOCs is found to show a trend that is direction independent. Moreover, the adsorption of VOCs on monolayer BP is strong enough to resist thermal disturbance, yet allows fast recovery time. The results suggest that BP is a compelling and feasible candidate for sensing applications of VOCs.
关键词： density functional theory calculations,gas sensors,black phosphorus,volatile organic compounds,non-equilibrium Green’s function formalism
更新于2025-09-23 15:22:29
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The maximum rectification ratio of pyrene-based molecular devices: a systematic study
摘要： We apply the NEGF + DFT technique to study the effect of anchoring groups on the electronic transport properties of a single pyrene molecule attached to two Au electrodes via three different anchoring groups (namely NO2, NH2 and CN). More specifically, we investigate the effect of asymmetric electrode coupling together with B and N doping on rectification ratio of a pyrene-based molecular device. The results indicate that the rectification ratio can be tuned by selecting configurations of maximum difference in the coupling parameters in the two sides of the gold electrodes, and its magnitude depends on the strength of the electronic coupling of the pyrene molecule to the gold electrodes. In addition, we observe that doping the molecule with B and N atoms decreases the coupling parameters by creating a resonant peak close to the Fermi level.
关键词： Non-equilibrium Green's function method,Molecular junction,Pyrene,Doping,Rectification ratio
更新于2025-09-19 17:15:36
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Theoretical study of the effects of electron-phonon and electron-photon interaction in optoelectronic properties of armchair graphene nano-flakes –A renormalization method
摘要： In this work, we study the effects of electron-phonon and electron-photon interaction on the electronic and optoelectronic properties of nano systems consisting of graphene nano-flakes (small length armchair graphene nanoribbons) connected to two semi-infinite metal electrodes. Our calculations are based on theuse of non-equilibrium Green’s function formalism. The non-interacting Hamiltonian is written within the nearest neighbor tight binding approximation. The full interacting Hamiltonian is then obtained by addition the electron-phonon and electron –photon interaction to the above non-interacting Hamiltonian .Using unitary transformations the interacting Hamiltonian is renormalized into a non-interacting tight-binding form with effective onsite energy and hopping parameter which contain the interacting effects . The Landuer-Buttiker formalism can now be used for the system with renormalized non-interacting Hamiltonian for calculating the electronic current. Within the above framework, we calculate the electron current, density of states (DOS) and photocurrent in the presence and absence of electron-phonon interaction in a nano-system consisting of graphene nano-flake with different width as central molecule. Our results show that electron-phonon interaction leads to decreasing the number of peaks in the DOS. Also the photocurrent has oscillatory behavior versus electron-photon coupling for different widths of the nano-flake. Finally, incident photon energy dependence of threshold electron-photon coupling (i.e photocurrent becomes larger than Ballistic case) and its increasing trend versus photon energy are studied.
关键词： Nearest neighbor tight binding aproximation,Landuer-Buttiker formalism,threshold electron-photon coupling,unitary transformations,electron-phonon and electron-photon interactions,graphene nano-flakes,Holstein model,Non-equilibrium Green’s function
更新于2025-09-12 10:27:22
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Design of graphene waveguides: Effect of edge orientation and waveguide configuration
摘要： Electron transport in a graphene quantum well can be analogous to photon transmission in an optical fiber. In this work, we present a detailed theoretical analysis to study the transport characteristics of graphene waveguides under the influence of different edge orientations. The non-equilibrium Green’s function approach in combination with the tight-binding Hamiltonian has been utilized to investigate the conductance properties of straight armchair and zigzag oriented graphene waveguides. Conductance plateaus at integer steps of 4e2/h have been observed in both orientations while the zigzag oriented waveguides present a wider first quantized plateau compared to that in the armchair oriented ones. Using various geometric and physical parameters, including side-barrier and waveguide width, and the metallic properties of terminals, we investigate the conductance profile of waveguides. In addition to the observation of valley symmetry in both edge orientations, this article explores the critical influence of drain contacts on waveguide conductance. Furthermore, we extended our transport study to three different highly bent waveguide configurations, such as U-shape, L-shape, and split-shape waveguides, in order to explore their applications in graphene-based ballistic integrated circuit devices. In the end, we also calculated the conductance of larger graphene waveguides using the scalable tight-binding model, in order to compare the results obtained from the original model.
关键词： non-equilibrium Green’s function,graphene waveguides,edge orientation,tight-binding Hamiltonian,conductance quantization
更新于2025-09-12 10:27:22
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[IEEE 2019 IEEE International Conference on Design & Test of Integrated Micro & Nano-Systems (DTS) - Gammarth-Tunis, Tunisia (2019.4.28-2019.5.1)] 2019 IEEE International Conference on Design & Test of Integrated Micro & Nano-Systems (DTS) - Fast and Accurate Simulation of Ultrascaled Carbon Nanotube Field-Effect Transistor Using ANN Sub-Modeling Technique
摘要： In this paper, we have proposed a new modeling methodology based on the artificial neural networks (ANN) to simulate the ultra-scaled carbon nanotube field-effect transistor (CNTFET). The sub-modeling concept has been employed to efficiently simplify the overall modeling process. The developed sub-models have been compared with the mode space non- equilibrium Green’s function ( MS-NEGF) simulations in terms of the resulted drain current, where a good agreement has been recorded. In addition, simulation tests have shown that the proposed smart models are faster of about two order of magnitude over the standard MS-NEGF simulation. The obtained results indicate that the proposed ANN-based sub- modeling is an accurate and computationally efficient approach, which can be successfully used to simulate, analyze, and optimize the ultra-scaled CNTFETs and the futuristic CNT-based nanoscale integrated circuits.
关键词： computational intelligence,Artificial neural networks (ANN),non-equilibrium Green’s function (NEGF),numerical modeling,carbon nanotube (CNTFET)
更新于2025-09-12 10:27:22
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Tiny nano-scale junction built on B/N doped single carbon nanotube
摘要： The characteristic sizes of carbon nanotube (CNT) based devices are constantly reduced. However, the continuous miniaturization is still facing many problems and requires innovative ideas and structures. By regular doping Boron and Nitrogen atoms in a semiconducting single-wall carbon nanotube (SWCNT), we have constructed an nano-scale junction with rectifying characteristics. The I-V curve of our junction resembles the I-V curve of an ideal diode with a p-n junction. This junction channel is about 0.6nm wide and 3.4nm long, and the footprint is 5.1nm long. Under 0.5V bias, the junction has a leakage current of -8.81×10-3 μA, a rectifying ratio Ion/Ioff of 0.716×103, and a current density of 10.52 mA/μm. Also, our study shows that how different dopant distribution influence I-V curve. Such a nano-scale regular doping method is effective and important, compared with the traditional random doping method.
关键词： B/N doped junction,I-V curve,density functional theory,non-equilibrium Green’s function,carbon nanotube,regular doping,electronic transport
更新于2025-09-11 14:15:04
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Electron transport in ladder-shaped graphene cuts
摘要： We numerically investigate electrical conductance of ladder-shaped graphene cuts (LGCs). Our calculations are performed by using non-equilibrium Green’s function method, in the nearest neighbor tight binding approximation. Our findings reveal strong sensitivity of electron transport through side rails of LGC to number, length and width of its rungs. Adding more rungs to ladder destroys the transport process in side rails. By lengthening the rungs transmission increases and finally tends to a constant value. Rungs widening has also destructive effect on electron transport via side rails. The results show that the transport properties of the LGC could be tuned via changing its structure, to discover transition from metal to insulator and vice versa. We also find that, lengthening of the ladder decreases transport along its side rails.
关键词： Electron transport,Ladder-shaped graphene cut,Non-equilibrium Green’s function
更新于2025-09-10 09:29:36