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Articles 31 - 60 of 365
Full-Text Articles in Nanoscience and Nanotechnology
Rate Equations From The Keldysh Formalism Applied To The Phonon Peak In Resonant-Tunneling Diodes, Roger Lake, Gerhard Klimeck, Supriyo Datta
Rate Equations From The Keldysh Formalism Applied To The Phonon Peak In Resonant-Tunneling Diodes, Roger Lake, Gerhard Klimeck, Supriyo Datta
Gerhard Klimeck
Starting from the Keldysh formalism, general analytical expressions are derived for the current and the occupation of the well in the presence of inelastic scattering, both at the main peak and at the pho- non peak. These expressions are then evaluated from a continuous coordinate representation of a double-barrier potential profile and also from a tight-binding model of a weakly coupled central site. The resulting expressions are similar, and the analytical expressions derived from the continuous coordi- nate representation compare well with the results obtained from numerical simulations. The analytical expressions and the numerical results show that unlike the main …
Atomistic Study Of Electronic Structure Of Pbse Nanowires, Abhijeet Paul, Gerhard Klimeck
Atomistic Study Of Electronic Structure Of Pbse Nanowires, Abhijeet Paul, Gerhard Klimeck
Gerhard Klimeck
Lead Selenide (PbSe) is an attractive ‘IV-VI’ semiconductor material to design optical sensors, lasers and thermoelectric devices. Improved fabrication of PbSe nanowires (NWs) enables the utilization of low dimensional quantum effects. The effect of cross-section size (W) and channel orientation on the bandstructure of PbSe NWs is studied using an 18 band sp3d5 tight-binding theory. The bandgap increases almost with the inverse of the W for all the orientations indicating a weak symmetry dependence. [111] and [110] NWs show higher ballistic conductance for the conduction and valence band compared to [100] NWs due to the significant splitting of the projected …
Performance Analysis Of Statistical Samples Of Graphene Nanoribbon Tunneling Transistors With Line Edge Roughness, Mathieu Luisier, Gerhard Klimeck
Performance Analysis Of Statistical Samples Of Graphene Nanoribbon Tunneling Transistors With Line Edge Roughness, Mathieu Luisier, Gerhard Klimeck
Gerhard Klimeck
Using a three-dimensional, atomistic quantum transport simulator based on the tight-binding method, we investigate statistical samples of single-gate graphene nanoribbon (GNR) tunneling field-effect transistors (TFETs) with different line edge roughness probabilities. We find that as the nanoribbon edges become rougher, the device OFF-current drastically increases due to a reduction of the graphene band gap and an enhancement of source-to-drain tunneling leakage through the gate potential barrier. At the same time, the ON-current remains almost constant. This leads to a deterioration of the transistor subthreshold slopes and to unacceptably low ON/OFF current ratios limiting the switching performances of GNR TFETs.
Spin-Valley Lifetimes In A Silicon Quantum Dot With Tunable Valley Splitting, C. H. Yang, A. Rossi, R. Ruskov, N. S. Lai, F. A. Mohiyaddin, S. Lee, C. Tahan, Gerhard Klimeck, A. Morello, A. S. Dzurak
Spin-Valley Lifetimes In A Silicon Quantum Dot With Tunable Valley Splitting, C. H. Yang, A. Rossi, R. Ruskov, N. S. Lai, F. A. Mohiyaddin, S. Lee, C. Tahan, Gerhard Klimeck, A. Morello, A. S. Dzurak
Gerhard Klimeck
Although silicon is a promising material for quantum computation, the degeneracy of the conduction band minima (valleys) must be lifted with a splitting sufficient to ensure the formation of well-defined and long-lived spin qubits. Here we demonstrate that valley separation can be accurately tuned via electrostatic gate control in a metal-oxide-semiconductor quantum dot, providing splittings spanning 0.3-0.8 meV. The splitting varies linearly with applied electric field, with a ratio in agreement with atomistic tight-binding predictions. We demonstrate single-shot spin read-out and measure the spin relaxation for different valley configurations and dot occupancies, finding one-electron lifetimes exceeding 2 s. Spin relaxation …
Engineered Valley-Orbit Splittings In Quantum-Confined Nanostructures In Silicon, Rajib Rahman, J. Verdujin, Neerav Kharche, Gabriel Lansbergen, Purdue University Gerhard Klimeck, Lloyd Hollenberg, Sven Rogge
Engineered Valley-Orbit Splittings In Quantum-Confined Nanostructures In Silicon, Rajib Rahman, J. Verdujin, Neerav Kharche, Gabriel Lansbergen, Purdue University Gerhard Klimeck, Lloyd Hollenberg, Sven Rogge
Gerhard Klimeck
An important challenge in silicon quantum electronics in the few electron regime is the poten- tially small energy gap between the ground and excited orbital states in 3D quantum confined nanostructures due to the multiple valley degeneracies of the conduction band present in silicon. Understanding the “valley-orbit” (VO) gap is essential for silicon qubits, as a large VO gap prevents leakage of the qubit states into a higher dimensional Hilbert space. The VO gap varies considerably depending on quantum confinement, and can be engineered by external electric fields. In this work we investigate VO splitting experimentally and theoretically in a …
Simulation Of Nanowire Tunneling Transistors: From The Wentzel-Kramers-Brillouin Approximation To Full-Band Phonon-Assisted Tunneling, Mathieu Luisier, Gerhard Klimeck
Simulation Of Nanowire Tunneling Transistors: From The Wentzel-Kramers-Brillouin Approximation To Full-Band Phonon-Assisted Tunneling, Mathieu Luisier, Gerhard Klimeck
Gerhard Klimeck
Nanowire band-to-band tunneling field-effect transistors TFETs are simulated using the Wentzel– Kramers–Brillouin WKB approximation and an atomistic, full-band quantum transport solver including direct and phonon-assisted tunneling PAT. It is found that the WKB approximation properly works if one single imaginary path connecting the valence band VB and the conduction band CB dominates the tunneling process as in direct band gap semiconductors. However, PAT is essential in Si and Ge nanowire TFETs where multiple, tightly-coupled, imaginary paths exist between the VB and the CB. © 2010 American Institute of Physics. doi:10.1063/1.3386521
Role Of Surface Orientation On Atomic Layer Deposited Al2o3/Gaas Interface Structure And Fermi Level Pinning: A Density Functional Theory Study, Ganesh Hegde, Gerhard Klimeck, Alejandro Strachan
Role Of Surface Orientation On Atomic Layer Deposited Al2o3/Gaas Interface Structure And Fermi Level Pinning: A Density Functional Theory Study, Ganesh Hegde, Gerhard Klimeck, Alejandro Strachan
Gerhard Klimeck
We investigate the initial surface reaction pathways in the atomic layer deposition (ALD) of Al2O3 on GaAs (111)A and (111)B substrates using precursors trimethylaluminum (TMA) and water to ascertain the effect of surface orientation on device performance. We find that the condition of the respective substrates prior to deposition of TMA and water has a major impact on the surface reactions that follow and on the resulting interface structure. The simulations explain the atomistic mechanism of the interfacial self-cleaning effect in ALD that preferentially removes As oxides. The electronic structure of the resulting atomic configurations indicates states throughout the bandgap …
Gate-Induced G-Factor Control And Dimensional Transition For Donors In Multivalley Semiconductors, Rajib Rahman, Seung H. Park, Timothy B. Boykin, Gerhard Klimeck, Sven Rogge, Lloyd Cl Hollenberg
Gate-Induced G-Factor Control And Dimensional Transition For Donors In Multivalley Semiconductors, Rajib Rahman, Seung H. Park, Timothy B. Boykin, Gerhard Klimeck, Sven Rogge, Lloyd Cl Hollenberg
Gerhard Klimeck
The dependence of the g factors of semiconductor donors on applied electric and magnetic fields is of immense importance in spin-based quantum computation and in semiconductor spintronics. The donor g-factor Stark shift is sensitive to the orientation of the electric and magnetic fields and is strongly influenced by the band-structure and spin-orbit interactions of the host. Using a multimillion atom tight-binding framework, the spin-orbit Stark parameters are computed for donors in multivalley semiconductors, silicon, and germanium. Comparison with limited experimental data shows good agreement for a donor in silicon. Results for gate-induced transition from three-dimensional to two-dimensional wave-function confinement show …
Resonant Tunneling Through Quantum Dot Arrays, Guanlong Chen, Gerhard Klimeck, Supriyo Datta, Guanhua Chen, William A. Goddard Iii
Resonant Tunneling Through Quantum Dot Arrays, Guanlong Chen, Gerhard Klimeck, Supriyo Datta, Guanhua Chen, William A. Goddard Iii
Gerhard Klimeck
We apply the Hubbard Hamiltonian to describe quantum-dot arrays weakly coupled to two contacts. Exact diagonalization is used to calculate the eigenstates of the arrays containing up to six dots and the linear-response conductance is then calculated as a function of the Fermi energy. In the atomic limit the conductance peaks form two distinct groups separated by the intradot Coulomb repulsion, while in the band limit the peaks occur in pairs. The crossover is studied. A finite interdot repulsion is found to cause interesting rearrangements in the conductance spectrum.
Design Space For Low Sensitivity To Size Variations In [110] Pmos Nanowire Devices: The Implications Of Anisotropy In The Quantization Mass, Neophytos Neophytou, Gerhard Klimeck
Design Space For Low Sensitivity To Size Variations In [110] Pmos Nanowire Devices: The Implications Of Anisotropy In The Quantization Mass, Neophytos Neophytou, Gerhard Klimeck
Gerhard Klimeck
A 20-band sp3d5s* spin-orbit-coupled, semiempirical, atomistic tight-binding model is used with a semiclassical, ballistic, field effect transistor (FET) model, to examine the ON-current variations to size variations of [110]-oriented PMOS nanowire devices. Infinitely long, uniform, rectangular nanowires of side dimensions from 3 to 12 nm are examined and significantly different behavior in width versus height variations are identified and explained. Design regions are identified, which show minor ON-current variations to significant width variations that might occur due to lack of line width control. Regions which show large ON-current variations to small height variations are also identified. The considerations of the …
Influence Of Cross-Section Geometry And Wire Orientation On The Phonon Shifts In Ultra-Scaled Si Nanowires, Abhijeet Paul, Mathieu Luisier, Gerhard Klimeck
Influence Of Cross-Section Geometry And Wire Orientation On The Phonon Shifts In Ultra-Scaled Si Nanowires, Abhijeet Paul, Mathieu Luisier, Gerhard Klimeck
Gerhard Klimeck
Engineering of the cross-section shape and size of ultra-scaled Si nanowires (SiNWs) provides an attractive way for tuning their structural properties. The acoustic and optical phonon shifts of the free-standing circular, hexagonal, square and triangular SiNWs are calculated using a Modified Valence Force Field (MVFF) model. The acoustic phonon blue shift (acoustic hardening) and the optical phonon red shift (optical softening) show a strong dependence on the cross-section shape and size of the SiNWs. The triangular SiNWs have the least structural symmetry as revealed by the splitting of the degenerate flexural phonon modes and The show the minimum acoustic hardening …
Electronic Structure Of Realistically Extended Atomistically Resolved Disordered Si:P Delta-Doped Layers, Sunhee Lee, Hoon Ryu, Lloyd Hollenberg, Michelle Simmons, Gerhard Klimeck
Electronic Structure Of Realistically Extended Atomistically Resolved Disordered Si:P Delta-Doped Layers, Sunhee Lee, Hoon Ryu, Lloyd Hollenberg, Michelle Simmons, Gerhard Klimeck
Gerhard Klimeck
The emergence of scanning tunneling microscope (STM) lithography and low temperature molecular beam epitaxy (MBE) opens the possibility of creating scalable donor based quantum computing architectures. In particular, atomically precise Si:P monolayer structures (delta-doped layers) serve as crucial contact regions and in-plane gates in single impurity devices. In this paper we study highly confined delta-doped layers to explain the disorder in the P dopant placements in realistically extended systems. The band structure is computed using the tight-binding formalism and charge-potential self-consistency. The exchange-correlation corrected impurity potential pulls down subbands below the silicon valley minima to create impurity bands. Our methodology …
Performance Comparisons Of Tunneling Field-Effect Transistors Made Of Insb, Carbon, And Gasb-Inas Broken Gap Heterostructures, Mathieu Luisier, Gerhard Klimeck
Performance Comparisons Of Tunneling Field-Effect Transistors Made Of Insb, Carbon, And Gasb-Inas Broken Gap Heterostructures, Mathieu Luisier, Gerhard Klimeck
Gerhard Klimeck
Band-to-band tunneling transistors (TFETs) made of InSb, Carbon, and GaSb-InAs broken gap heterostructures are simulated using an atomistic and full-band quantum transport solver. The performances of two-dimensional single-gate and double-gate devices as well as three-dimensional gate-all-around structures are analyzed and compared to find the most promising TFET design. All transistor types are able to provide a region with a steep subthreshold slope, but despite their low band gap, InSb- and C-based (graphene nanoribbons and carbon nanotubes) devices do not offer high enough ON-currents, contrary to GaSb-InAs broken gap structures. However, the nanoribbon and nanotube TFETs can operate at much lower …
Current Density And Continuity In Discretized Models, Timothy B. Boykin, Mathieu Luisier, Gerhard Klimeck
Current Density And Continuity In Discretized Models, Timothy B. Boykin, Mathieu Luisier, Gerhard Klimeck
Gerhard Klimeck
Discrete approaches have long been used in numerical modelling of physical systems in both research and teaching. Discrete versions of the Schr ¨ odinger equation employing either one or several basis functions per mesh point are often used by senior undergraduates and beginning graduate students in computational physics projects. In studying discrete models, students can encounter conceptual difficulties with the representation of the current and its divergence because different finite-difference expressions, all of which reduce to the current density in the continuous limit, measure different physical quantities. Understanding these different discrete currents is essential and requires a careful analysis of …
The Composite Materials Manufacturaing Hub - Crowd Sourcing As The Norm, R. Byron Pipes, Gerhard Klimeck, Mark R. Pipes
The Composite Materials Manufacturaing Hub - Crowd Sourcing As The Norm, R. Byron Pipes, Gerhard Klimeck, Mark R. Pipes
Gerhard Klimeck
The Composites Manufacturing HUB puts compo- sites manufacturing simulations in the hands of those who need them to invent new and innovative ways to capture the extraordinary benefits of these high perfor- mance products at an acceptable manufactured cost. The HUB provides the user simple browser access to power- ful tools that simulate the actual steps and outcome con- ditions of a complex manufacturing process without the need to download and maintain software in the conven- tional manner. Learning use of the manufacturing simu- lation tools will also be accomplished on the HUB in or- der to allow for continuous …
Feasibility, Accuracy, And Performance Of Contact Block Reduction Method For Multi-Band Simulations Of Ballistic Quantum Transport, Hoon Ryu, Hong-Hyun Park, Mincheol Shin, Dragica Vasileska, Gerhard Klimeck
Feasibility, Accuracy, And Performance Of Contact Block Reduction Method For Multi-Band Simulations Of Ballistic Quantum Transport, Hoon Ryu, Hong-Hyun Park, Mincheol Shin, Dragica Vasileska, Gerhard Klimeck
Gerhard Klimeck
Numerical utilities of the contact block reduction (CBR) method in evaluating the retarded Green’s function are discussed for 3D multi-band open systems that are represented by the atomic tight-binding (TB) and continuum k * p (KP) band model. It is shown that the methodology to approximate solutions of open systems, which has been already reported for the single-band effective mass model, cannot be directly used for atomic TB systems, since the use of a set of zinc blende crystal grids makes the inter-coupling matrix non-invertible. We derive and test an alternative with which the CBR method can be still practical …
Atomistic Full-Band Simulations Of Si Nanowire Transistors: Effects Of Electron-Phonon Scattering, Mathieu Luisier, Gerhard Klimeck
Atomistic Full-Band Simulations Of Si Nanowire Transistors: Effects Of Electron-Phonon Scattering, Mathieu Luisier, Gerhard Klimeck
Gerhard Klimeck
An atomistic full-band quantum transport simulator has been developed to study three-dimensional Si nanowire field-effect transistors (FETs) in the presence of electron-phonon scattering. The Non-equilibrium Green's Function (NEGF) formalism is solved in a nearest-neighbor sp(3)d(5)s* tight-binding basis. The scattering self-energies are derived in the self-consistent Born approximation to inelastically couple the full electron and phonon energy spectra. The band dispersion and the eigenmodes of the confined phonons are calculated using a dynamical matrix that includes the bond and angle deformations of the nanowires. The optimization of the numerical algorithms and the parallelization of the NEGF scheme enable the investigation of …
On The Validity Of The Top Of The Barrier Quantum Transport Model For Ballistic Nanowire Mosfets, Abhijeet Paul, Saumitra Mehrotra, Gerhard Klimeck, Mathieu Luisier
On The Validity Of The Top Of The Barrier Quantum Transport Model For Ballistic Nanowire Mosfets, Abhijeet Paul, Saumitra Mehrotra, Gerhard Klimeck, Mathieu Luisier
Gerhard Klimeck
This work focuses on the determination of the valid device domain for the use of the Top of the barrier (ToB) model to simulate quantum transport in nanowire MOSFETs in the ballistic regime. The presence of a proper Source/Drain barrier in the device is an important criterion for the applicability of the model. Long channel devices can be accurately modeled under low and high drain bias with DIBL adjustment.
Cyber-Enabled Simulations In Nanoscale Science And Engineering Introduction, Alejandro Strachan, Gerhard Klimeck, Mark S. Lundstrom
Cyber-Enabled Simulations In Nanoscale Science And Engineering Introduction, Alejandro Strachan, Gerhard Klimeck, Mark S. Lundstrom
Gerhard Klimeck
Editorial Material
From Nemo1d And Nemo3d To Omen: Moving Towards Atomistic 3-D Quantum Transport In Nano-Scale Semiconductors, Gerhard Klimeck, Mathieu Luisier
From Nemo1d And Nemo3d To Omen: Moving Towards Atomistic 3-D Quantum Transport In Nano-Scale Semiconductors, Gerhard Klimeck, Mathieu Luisier
Gerhard Klimeck
Lessons learned in 15 years of NEMO development starting from quantitative and predictive resonant tunneling diode (RTD) to multi-million atom electronic structure modeling and the path for OMEN are laid out. The recent OMEN capabilities enable realistically large 3D atomistic nano-scale device simulation.
Sub-Threshold Study Of Undoped Trigate Nfinfet, G C. Tettamanzi, G P. Lansbergen, A Paul, Sunhee Lee, P A. Deosarran, N Collaert, Gerhard Klimeck, S Biesemans, S Rogge
Sub-Threshold Study Of Undoped Trigate Nfinfet, G C. Tettamanzi, G P. Lansbergen, A Paul, Sunhee Lee, P A. Deosarran, N Collaert, Gerhard Klimeck, S Biesemans, S Rogge
Gerhard Klimeck
Modern MOSFET devices with undoped channel have a non-trivial current distribution, which is gate voltage dependent In our work we have studied the sub-threshold behavior of undoped triple gate MOSFETs (FinFETs) using a thermionic transport model We have analyzed the conductance data of such devices. and from this, we have been able to determine the evolution of both the active cross-section area of the channel and the barrier height as a function of the gate voltage The result of our experiments shows good agreement with tight binding simulations and with analytical results. This confirms the validity of the use of …
Effects Of Interface Roughness Scattering On Radio Frequency Performance Of Silicon Nanowire Transistors, Sunggeun Kim, Mathieu Luisier, Timothy B. Boykin, Gerhard Klimeck
Effects Of Interface Roughness Scattering On Radio Frequency Performance Of Silicon Nanowire Transistors, Sunggeun Kim, Mathieu Luisier, Timothy B. Boykin, Gerhard Klimeck
Gerhard Klimeck
The effects of an atomistic interface roughness in n-type silicon nanowire transistors (SiNWT) on the radio frequency performance are analyzed. Interface roughness scattering (IRS) is statistically investigated through a three dimensional full–band quantum transport simulation based on the sp3d5s∗ tight–binding model. As the diameter of the SiNWT is scaled down below 3 nm, IRS causes a significant reduction of the cut-off frequency. The fluctuations of the conduction band edge due to the rough surface lead to a reflection of electrons through mode-mismatch. This effect reduces the velocity of electrons and hence the transconductance considerably causing a cut-off frequency reduction.
Advancing Nanoelectronic Device Modeling Through Peta-Scale Computing And Deployment On Nanohub, Benjamin Haley, Sunhee Lee, Mathieu Luisier, Hoon Ryu, Faisal Saied, Steven Clark, Hansang Bae, Gerhard Klimeck
Advancing Nanoelectronic Device Modeling Through Peta-Scale Computing And Deployment On Nanohub, Benjamin Haley, Sunhee Lee, Mathieu Luisier, Hoon Ryu, Faisal Saied, Steven Clark, Hansang Bae, Gerhard Klimeck
Gerhard Klimeck
Recent improvements to existing HPC codes NEMO 3-D and OMEN, combined with access to peta-scale computing resources, have enabled realistic device engineering simulations that were previously infeasible. NEMO 3-D can now simulate 1 billion atom systems, and, using 3D spatial decomposition, scale to 32768 cores. Simulation time for the band structure of an experimental P doped Si quantum computing device fell from 40 minutes to I minute. OMEN can perform fully quantum mechanical transport calculations for real-word UTB FETs on 147,456 cores in roughly 5 minutes. Both of these tools power simulation engines on the nanoHUB, giving the community access …
New Tools For The Direct Characterisation Of Finfets, G. C. Tettamanzi, A. Paul, S. Lee, Gerhard Klimeck, S. Rogge
New Tools For The Direct Characterisation Of Finfets, G. C. Tettamanzi, A. Paul, S. Lee, Gerhard Klimeck, S. Rogge
Gerhard Klimeck
This paper discusses how classical transport theories such as the thermionic emission (Ref. [1]), can be used as a powerful tool for the study and the understanding of the most complex mechanisms of transport in Fin Field Effect Transistors (FinFETs). By means of simple current and differential conductance measurements, taken at different temperatures and different gate voltages (VG's), it is possible to extrapolate the evolution of important parameters such as the spatial region of transport and the height of thermionic barrier at the centre of the channel. Furthermore, if the measurements are used in conjunction with simulated data, it becomes …
Orbital Start Effect And Quantum Confinement Transition Of Donors In Silicon, Rajib Rahman, G. P. Lansbergen, Seung H. Park, J. Verdujin, Gerhard Klimeck, S. Rogge, Lloyd C. L. Hollenberg
Orbital Start Effect And Quantum Confinement Transition Of Donors In Silicon, Rajib Rahman, G. P. Lansbergen, Seung H. Park, J. Verdujin, Gerhard Klimeck, S. Rogge, Lloyd C. L. Hollenberg
Gerhard Klimeck
Adiabatic shuttling of single impurity bound electrons to gate-induced surface states in semiconductors has attracted much attention in recent times, mostly in the context of solid-state quantum computer architecture. A recent transport spectroscopy experiment for the first time was able to probe the Stark shifted spectrum of a single donor in silicon buried close to a gate. Here, we present the full theoretical model involving large-scale quantum mechanical simulations that was used to compute the Stark shifted donor states in order to interpret the experimental data. Use of atomistic tight-binding technique on a domain of over a million atoms helped …
Level Spectrum Of Single Gated As Donors, Gabriel P. Lansbergen, Rajib Rahman, J. Caro, N. Collaert, S. Biesemans, Gerhard Klimeck, S. Rogge, L.C. L. Hollenberg
Level Spectrum Of Single Gated As Donors, Gabriel P. Lansbergen, Rajib Rahman, J. Caro, N. Collaert, S. Biesemans, Gerhard Klimeck, S. Rogge, L.C. L. Hollenberg
Gerhard Klimeck
We study the electrical transport through single As donors incorporated in the channel of a FinFET, i.e. a donor in a three-terminal geometry. By means of spectroscopic measurements in conjuction with a NEMO-3D model, we can identify the excited states and associate them with either the donors Coulomb potential, a triangular well at the interface or a hybridized combination of the two. The correspondence between the transport measurements, the theoretical model and the local environment provides an atomic understanding of actual gated donors in a nanostructure.
Effects Of Interface Disorder On Valley Splitting In Sige/Si/Sige Quantum Wells, Zhengping Jiang, Neerav Kharche, Timothy Boykin, Gerhard Klimeck
Effects Of Interface Disorder On Valley Splitting In Sige/Si/Sige Quantum Wells, Zhengping Jiang, Neerav Kharche, Timothy Boykin, Gerhard Klimeck
Gerhard Klimeck
A sharp potential barrier at the Si/SiGe interface introduces valley splitting (VS), which lifts the 2-fold valley degeneracy in strained SiGe/Si/SiGe quantum wells (QWs). This work examines in detail the effects of Si/SiGe interface disorder on the VS in an atomistic tight binding approach based on statistical sampling. VS is analyzed as a function of electric field, QW thickness, and simulation domain size. Strong electric fields push the electron wavefunctions into the SiGe buffer and introduce significant VS fluctuations from device to device. A Gedankenexperiment with ordered alloys sheds light on the importance of different bonding configurations on VS. We …
Structures And Energetics Of Silicon Nanotubes From Molecular Dynamics And Density Functional Theory, Amritanshu Palaria, Gerhard Klimeck, Alejandro Strachan
Structures And Energetics Of Silicon Nanotubes From Molecular Dynamics And Density Functional Theory, Amritanshu Palaria, Gerhard Klimeck, Alejandro Strachan
Gerhard Klimeck
We use molecular dynamics with a first-principles-based force field and density functional theory to predict the atomic structure, energetics, and elastic properties of Si nanotubes. We find various low-energy and low-symmetry hollow structures with external diameters of about 1 nm. These are the most stable structures in this small-diameter regime reported so far and exhibit properties very different from the bulk. While the cohesive energies of the four most stable nanotubes reported here are similar (from 0.638 to 0.697 eV above bulk Si), they have disparate Young's moduli (from 72 to 123 GPa).
Non-Primitive Rectangular Cells For Tight-Binding Electronic Structure Calculations, Timothy Boykin, Neerav Kharche, Gerhard Klimeck
Non-Primitive Rectangular Cells For Tight-Binding Electronic Structure Calculations, Timothy Boykin, Neerav Kharche, Gerhard Klimeck
Gerhard Klimeck
Rectangular non-primitive unit cells are computationally convenient for use in nanodevice electronic structure and transport calculations. When these cells are used for Calculations of structures with periodicity, the resulting bands are zone-folded and must be unfolded in order to identify important gaps and masses. Before the zone-unfolding method can be applied, one must first determine the allowed wavevectors for the specific non-primitive cell. Because most computationally convenient non-primitive cells do not have axes parallel to the primitive cell direct lattice vectors, finding the allowed wavevectors is generally a non-trivial task. (Solid state texts generally treat only the simplest case in …
Distributed Negf Algorithms For The Simulation Of Nanoelectronic Devices With Scattering, Stephen Cauley, Mathieu Luisier, Venkataramanan Balakrishnan, Gerhard Klimeck, Cheng-Kok Koh
Distributed Negf Algorithms For The Simulation Of Nanoelectronic Devices With Scattering, Stephen Cauley, Mathieu Luisier, Venkataramanan Balakrishnan, Gerhard Klimeck, Cheng-Kok Koh
Gerhard Klimeck
Through the Non-Equilibrium Green’s Function (NEGF) formalism, quantum- scale device simulation can be performed with the inclusion of electron-phonon scattering. However, the simulation of realistically sized devices under the NEGF formalism typically requires prohibitive amounts of memory and computation time. Two of the most demanding computational problems for NEGF simulation involve mathematical operations with structured matrices called semiseparable matrices. In this work, we present parallel approaches for these computational problems which allow for efficient distribution of both memory and computation based upon the underlying device structure. This is critical when simulating realistically sized devices due to the aforementioned computational burdens. …