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[Advances in Intelligent Systems and Computing] Modelling and Simulation in Science, Technology and Engineering Mathematics Volume 749 (Proceedings of the International Conference on Modelling and Simulation (MS-17)) || Computation of Current Density in Double Well Resonant Tunneling Diode Using Self-consistency Technique
摘要： Double well resonant tunneling diode is analytically simulated for different constituent layer widths, and also for different operating temperatures. Peak current densities are obtained at particular bias values, which speak for eigenstates alignment between adjacent quantum wells. Self-consistency technique is incorporated for simulation purpose which provides accurate result regarding the position of the peaks, optimum structural parameters in order to obtain that magnitude, and the junction temperature to obtain measurable current at the applied bias range. It may also be noted that current increases with increase in temperature. Two different dimension set are used for simulation in order to reveal the external influence on electrical properties of the device. Different dimensions of contact regions also help to analyze fluctuations in peak current profile. Thus the device can be operated at those biasing points, where peaks are appeared.
关键词： Resonant tunneling diode,Self-consistency technique,Quantum transport,Current density,Semiconductor heterostructures
更新于2025-09-09 09:28:46
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Distribution of waiting times between electron cotunneling events
摘要： In the resonant tunneling regime, sequential processes dominate single-electron transport through quantum dots or molecules that are weakly coupled to macroscopic electrodes. In the Coulomb blockade regime, however, cotunneling processes dominate. Cotunneling is an inherently quantum phenomenon and thus gives rise to interesting observations, such as an increase in the current shot noise. Since cotunneling processes are inherently fast compared to the sequential processes, it is of interest to examine the short time behavior of systems where cotunneling plays a role, and whether these systems display nonrenewal statistics. We consider three questions in this paper. Given that an electron has tunneled from the source to the drain via a cotunneling or sequential process, what is the waiting time until another electron cotunnels from the source to the drain? What are the statistical properties of these waiting time intervals? How does cotunneling affect the statistical properties of a system with strong inelastic electron-electron interactions? In answering these questions, we extend the existing formalism for waiting time distributions in single-electron transport to include cotunneling processes via an n-resolved Markovian master equation. We demonstrate that for a single resonant level, the analytic waiting time distribution including cotunneling processes yields information on individual tunneling amplitudes. For both a SRL and an Anderson impurity deep in the Coulomb blockade, there is a nonzero probability for two electrons to cotunnel to the drain with zero waiting time in between. Furthermore, we show that at high voltages, cotunneling processes slightly modify the nonrenewal behavior of an Anderson impurity with a strong inelastic electron-electron interaction.
关键词： waiting time distribution,quantum transport,electron cotunneling,Markovian master equation,Coulomb blockade
更新于2025-09-09 09:28:46
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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) - Toward more realistic NEGF simulations of vertically stacked multiple SiNW FETs
摘要： We present quantum transport simulation results of vertically stacked multiple silicon nanowire (SiNW) FETs based on the non-equilibrium Green’s function (NEGF) method. In order to consider more realistic device conditions such as complex geometry of the multi-channel FETs and various carrier scattering processes, we improved physical models and numerical techniques for the NEGF simulations.
关键词： non-equilibrium Green’s function (NEGF),quantum transport,multiple nanowire FET
更新于2025-09-09 09:28:46
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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) - Advanced Algorithms for Ab-initio Device Simulations
摘要： Numerical algorithms dedicated to large-scale quantum transport problems from first-principles are presented in this paper. They can be decomposed into three main categories: (i) the calculation of the open boundary conditions that connect the simulation domain and its environment, (ii) the solution of the resulting Schr?dinger equation in the ballistic limit of transport, and (iii) the extension of this case to situations involving scattering, e.g. electron-phonon interactions. It will be shown that ab-initio device simulations require algorithms specifically developed for that purpose and that graphics processing units (GPUs) can bring significant speed ups as compared to solvers based on CPUs only. As an illustration, the computational times coming from the investigation of a realistic conductive bridging random access memory cell will be reported.
关键词： DFT,algorithms,NEGF,quantum transport
更新于2025-09-09 09:28:46
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On the existence of superradiant excitonic states in microtubules
摘要： Microtubules are biological protein polymers with critical and diverse functions. Their structures share some similarities with photosynthetic antenna complexes, particularly in the ordered arrangement of photoactive molecules with large transition dipole moments. As the role of photoexcitations in microtubules remains an open question, here we analyze tryptophan molecules, the amino acid building block of microtubules with the largest transition dipole strength. By taking their positions and dipole orientations from realistic models capable of reproducing tubulin experimental spectra, and using a Hamiltonian widely employed in quantum optics to describe light-matter interactions, we show that such molecules arranged in their native microtubule configuration exhibit a superradiant lowest exciton state, which represents an excitation fully extended on the chromophore lattice. We also show that such a superradiant state emerges due to supertransfer coupling between the lowest exciton states of smaller blocks of the microtubule. In the dynamics we find that the spreading of excitation is ballistic in the absence of external sources of disorder and strongly dependent on initial conditions. The velocity of photoexcitation spreading is shown to be enhanced by the supertransfer effect with respect to the velocity one would expect from the strength of the nearest-neighbor coupling between tryptophan molecules in the microtubule. Finally, such structures are shown to have an enhanced robustness to static disorder when compared to geometries that include only short-range interactions. These cooperative effects (superradiance and supertransfer) may induce ultra-efficient photoexcitation absorption and could enhance excitonic energy transfer in microtubules over long distances under physiological conditions.
关键词： quantum transport in disordered systems,energy transfer,open quantum systems,quantum biology
更新于2025-09-04 15:30:14
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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) - Efficient Modeling of Electron Transport with Plane Waves
摘要： We present a method to simulate ballistic quantum transport in one-dimensional nanostructures, such as extremely scaled transistors, with a channel of nanowires or nanoribbons. In contrast to most popular approaches, we develop our method employing an accurate plane-wave basis at the atomic scale while retaining the numerical ef?ciency of a localized (tight-binding) basis at larger scales. At the core of our method is a ?nite-element expansion, where the ?nite element basis is enriched by a set of Bloch waves at high-symmetry points in the Brillouin zone of the crystal. We demonstrate the accuracy and ef?ciency of our method with the self-consistent simulation of ballistic transport in graphene nanoribbon FETs.
关键词： graphene nanoribbon FETs,Bloch waves,finite-element expansion,plane-wave basis,ballistic quantum transport
更新于2025-09-04 15:30:14