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Gerhard Klimeck - One of the best experts on this subject based on the ideXlab platform.
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transferable Tight Binding Model for strained group iv and iii v materials and heterostructures
Physical Review B, 2016Co-Authors: Yaohua Tan, Michael Povolotskyi, Tillmann Kubis, Timothy B Boykin, Gerhard KlimeckAbstract:It is critical to capture the effect due to strain and material interface for device level transistor Modeling. We introduce a transferable $s{p}^{3}{d}^{5}{s}^{*}$ Tight-Binding Model with nearest-neighbor interactions for arbitrarily strained group IV and III-V materials. The Tight-Binding Model is parametrized with respect to hybrid functional (HSE06) calculations for varieties of strained systems. The Tight-Binding calculations of ultrasmall superlattices formed by group IV and group III-V materials show good agreement with the corresponding HSE06 calculations. The application of the Tight-Binding Model to superlattices demonstrates that the transferable Tight-Binding Model with nearest-neighbor interactions can be obtained for group IV and III-V materials.
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transferable Tight Binding Model for strained group iv and iii v heterostructures
Bulletin of the American Physical Society, 2016Co-Authors: Yaohua Tan, Michael Povolotskyi, Tillmann Kubis, Timothy B Boykin, Gerhard KlimeckAbstract:Modern semiconductor devices have reached critical device dimensions in the range of several nanometers. Devices such as superlattice-FETs[1],Ultra Thin Body(UTB)-FETs and FinFETs consist of strained materials with different lattice constant. Quantitative analysis of those devices requires the reliable prediction of the bandgaps, effective masses in strained heterostructures. The Empirical Tight Binding (ETB) methods are appropriate for atomistic device Modeling due to their numeric efficiency[2]. However, the accuracy of ETB calculations dependents on the transferability of the ETB parameters. In this work, transferable ETB parameters of strained IV and III-V group semiconductors are generated from ab-initio calculations[3], [4]. The ETB parameters show good transferability when applied to strained bulk materials as well as ultra-thin superlattices. ETB parameters are obtained through ab-initio mapping process[4]. During the parameterization process, ETB parameters and basis functions are adjusted to match the corresponding ab-initio band structures and wave functions. In this work, ab-initio bands of the strained bulk materials and superlattices are calculated using VASP. Hybrid functional HSE06 is used to produce correct band gaps. Group IV and III-V materials are parameterized using the sp3d5s* ETB Model. The parameterized group IV and III-V materials include Si, Ge, Si0.5Ge0.5 and compounds XY with X = Al,Ga and In, Y = P, As and Sb. To have transferable ETB parameters, following constraints are imposed. a) Onsites of each atom depend only on the atom type instead of materials. b) Both strained and unstrained ETB band structures are fitted to ab-initio results. c) Variation of interatomic coupling parameters among different materials is less than 0.3eV. The strain effect is included using strain induced onsite and interatomic couplings which depend on the change of bond lengths of the first nearest neighbours and bond angles between the first nearest neighbours. Band structures of Selected semiconductors (bulk Si, Ge, Si0.5Ge0.5, AlAs, GaAs and InAs) are shown in Fig. 1. The ETB band structures match the corresponding hybrid functional calculations results well. Compared with corresponding HSE06 results, band edge at high symmetry points are within 0.05eV and important effective masses have less than 10% error. Fig. 2 and 3 show InAs and Si conduction and valence band edge splitting under strains produced by stress along 001 and 111 directions. The splitting of conduction and valence band edges at high symmetry points such as Γ, L and X are correctly captured by the strain Model. Fig. 4 and Fig. 5 show the band structure of GaAs/AlAs and Si/Ge superlattices respectively. The TB band structure agree with the HSE06 bands, demonstrating good transferability of ETB parameters for group IV and III-V semiconductors. The use of nanoHUB.org computational resources operated by the Network for Computational Nanotechnology funded by the US National Science Foundation under Grant Nos. EEC-0228390, EEC-1227110, EEC0228390, EEC-0634750, OCI-0438246, OCI-0832623 and OCI-0721680 is gratefully acknowledged.
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transferable Tight Binding Model for strained group iv and iii v heterostructures
arXiv: Materials Science, 2015Co-Authors: Yaohua Tan, Michael Povolotskyi, Tillmann Kubis, Timothy B Boykin, Gerhard KlimeckAbstract:In this work, transferable empirical Tight Binding parameters of strained group IV and III-V semiconductors are generated from ab-initio calculations. The empirical Tight Binding parameters show good transferability when applied to strained bulk materials as well as ultra-thin superlattices.
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an environment dependent semi empirical Tight Binding Model suitable for electron transport in bulk metals metal alloys metallic interfaces and metallic nanostructures ii application effect of quantum confinement and homogeneous strain on cu conductance
Journal of Applied Physics, 2014Co-Authors: Ganesh Hegde, Michael Povolotskyi, Tillmann Kubis, James Charles, Gerhard KlimeckAbstract:The Semi-Empirical Tight Binding Model developed in Part I Hegde et al. [J. Appl. Phys. 115, 123703 (2014)] is applied to metal transport problems of current relevance in Part II. A systematic study of the effect of quantum confinement, transport orientation, and homogeneous strain on electronic transport properties of Cu is carried out. It is found that quantum confinement from bulk to nanowire boundary conditions leads to significant anisotropy in conductance of Cu along different transport orientations. Compressive homogeneous strain is found to reduce resistivity by increasing the density of conducting modes in Cu. The [110] transport orientation in Cu nanowires is found to be the most favorable for mitigating conductivity degradation since it shows least reduction in conductance with confinement and responds most favorably to compressive strain.
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accurate six band nearest neighbor Tight Binding Model for the π bands of bulk graphene and graphene nanoribbons
Journal of Applied Physics, 2011Co-Authors: Timothy B Boykin, Gerhard Klimeck, Mathieu Luisier, Xueping Jiang, Neerav Kharche, Yu Zhou, Saroj K NayakAbstract:Accurate Modeling of the π-bands of armchair graphene nanoribbons (AGNRs) requires correctly reproducing asymmetries in the bulk graphene bands, as well as providing a realistic Model for hydrogen passivation of the edge atoms. The commonly used single-pz orbital approach fails on both these counts. To overcome these failures we introduce a nearest-neighbor, three orbital per atom p/d Tight-Binding Model for graphene. The parameters of the Model are fit to first-principles density-functional theory –based calculations as well as to those based on the many-body Green’s function and screened-exchange formalism, giving excellent agreement with the ab initio AGNR bands. We employ this Model to calculate the current-voltage characteristics of an AGNR MOSFET and the conductance of rough-edge AGNRs, finding significant differences versus the single-pz Model. These results show that an accurate band structure Model is essential for predicting the performance of graphene-based nanodevices.
Timothy B Boykin - One of the best experts on this subject based on the ideXlab platform.
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transferable Tight Binding Model for strained group iv and iii v materials and heterostructures
Physical Review B, 2016Co-Authors: Yaohua Tan, Michael Povolotskyi, Tillmann Kubis, Timothy B Boykin, Gerhard KlimeckAbstract:It is critical to capture the effect due to strain and material interface for device level transistor Modeling. We introduce a transferable $s{p}^{3}{d}^{5}{s}^{*}$ Tight-Binding Model with nearest-neighbor interactions for arbitrarily strained group IV and III-V materials. The Tight-Binding Model is parametrized with respect to hybrid functional (HSE06) calculations for varieties of strained systems. The Tight-Binding calculations of ultrasmall superlattices formed by group IV and group III-V materials show good agreement with the corresponding HSE06 calculations. The application of the Tight-Binding Model to superlattices demonstrates that the transferable Tight-Binding Model with nearest-neighbor interactions can be obtained for group IV and III-V materials.
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transferable Tight Binding Model for strained group iv and iii v heterostructures
Bulletin of the American Physical Society, 2016Co-Authors: Yaohua Tan, Michael Povolotskyi, Tillmann Kubis, Timothy B Boykin, Gerhard KlimeckAbstract:Modern semiconductor devices have reached critical device dimensions in the range of several nanometers. Devices such as superlattice-FETs[1],Ultra Thin Body(UTB)-FETs and FinFETs consist of strained materials with different lattice constant. Quantitative analysis of those devices requires the reliable prediction of the bandgaps, effective masses in strained heterostructures. The Empirical Tight Binding (ETB) methods are appropriate for atomistic device Modeling due to their numeric efficiency[2]. However, the accuracy of ETB calculations dependents on the transferability of the ETB parameters. In this work, transferable ETB parameters of strained IV and III-V group semiconductors are generated from ab-initio calculations[3], [4]. The ETB parameters show good transferability when applied to strained bulk materials as well as ultra-thin superlattices. ETB parameters are obtained through ab-initio mapping process[4]. During the parameterization process, ETB parameters and basis functions are adjusted to match the corresponding ab-initio band structures and wave functions. In this work, ab-initio bands of the strained bulk materials and superlattices are calculated using VASP. Hybrid functional HSE06 is used to produce correct band gaps. Group IV and III-V materials are parameterized using the sp3d5s* ETB Model. The parameterized group IV and III-V materials include Si, Ge, Si0.5Ge0.5 and compounds XY with X = Al,Ga and In, Y = P, As and Sb. To have transferable ETB parameters, following constraints are imposed. a) Onsites of each atom depend only on the atom type instead of materials. b) Both strained and unstrained ETB band structures are fitted to ab-initio results. c) Variation of interatomic coupling parameters among different materials is less than 0.3eV. The strain effect is included using strain induced onsite and interatomic couplings which depend on the change of bond lengths of the first nearest neighbours and bond angles between the first nearest neighbours. Band structures of Selected semiconductors (bulk Si, Ge, Si0.5Ge0.5, AlAs, GaAs and InAs) are shown in Fig. 1. The ETB band structures match the corresponding hybrid functional calculations results well. Compared with corresponding HSE06 results, band edge at high symmetry points are within 0.05eV and important effective masses have less than 10% error. Fig. 2 and 3 show InAs and Si conduction and valence band edge splitting under strains produced by stress along 001 and 111 directions. The splitting of conduction and valence band edges at high symmetry points such as Γ, L and X are correctly captured by the strain Model. Fig. 4 and Fig. 5 show the band structure of GaAs/AlAs and Si/Ge superlattices respectively. The TB band structure agree with the HSE06 bands, demonstrating good transferability of ETB parameters for group IV and III-V semiconductors. The use of nanoHUB.org computational resources operated by the Network for Computational Nanotechnology funded by the US National Science Foundation under Grant Nos. EEC-0228390, EEC-1227110, EEC0228390, EEC-0634750, OCI-0438246, OCI-0832623 and OCI-0721680 is gratefully acknowledged.
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transferable Tight Binding Model for strained group iv and iii v heterostructures
arXiv: Materials Science, 2015Co-Authors: Yaohua Tan, Michael Povolotskyi, Tillmann Kubis, Timothy B Boykin, Gerhard KlimeckAbstract:In this work, transferable empirical Tight Binding parameters of strained group IV and III-V semiconductors are generated from ab-initio calculations. The empirical Tight Binding parameters show good transferability when applied to strained bulk materials as well as ultra-thin superlattices.
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accurate six band nearest neighbor Tight Binding Model for the π bands of bulk graphene and graphene nanoribbons
Journal of Applied Physics, 2011Co-Authors: Timothy B Boykin, Gerhard Klimeck, Mathieu Luisier, Xueping Jiang, Neerav Kharche, Yu Zhou, Saroj K NayakAbstract:Accurate Modeling of the π-bands of armchair graphene nanoribbons (AGNRs) requires correctly reproducing asymmetries in the bulk graphene bands, as well as providing a realistic Model for hydrogen passivation of the edge atoms. The commonly used single-pz orbital approach fails on both these counts. To overcome these failures we introduce a nearest-neighbor, three orbital per atom p/d Tight-Binding Model for graphene. The parameters of the Model are fit to first-principles density-functional theory –based calculations as well as to those based on the many-body Green’s function and screened-exchange formalism, giving excellent agreement with the ab initio AGNR bands. We employ this Model to calculate the current-voltage characteristics of an AGNR MOSFET and the conductance of rough-edge AGNRs, finding significant differences versus the single-pz Model. These results show that an accurate band structure Model is essential for predicting the performance of graphene-based nanodevices.
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accurate six band nearest neighbor Tight Binding Model for the pi bands of bulk graphene and graphene nanoribbons
arXiv: Mesoscale and Nanoscale Physics, 2011Co-Authors: Timothy B Boykin, Gerhard Klimeck, Mathieu Luisier, Xueping Jiang, Neerav Kharche, Yu Zhou, Saroj K NayakAbstract:Accurate Modeling of the pi-bands of armchair graphene nanoribbons (AGNRs) requires correctly reproducing asymmetries in the bulk graphene bands as well as providing a realistic Model for hydrogen passivation of the edge atoms. The commonly used single-pz orbital approach fails on both these counts. To overcome these failures we introduce a nearest-neighbor, three orbital per atom p/d Tight-Binding Model for graphene. The parameters of the Model are fit to first-principles density-functional theory (DFT) - based calculations as well as to those based on the many-body Green's function and screened-exchange (GW) formalism, giving excellent agreement with the ab initio AGNR bands. We employ this Model to calculate the current-voltage characteristics of an AGNR MOSFET and the conductance of rough-edge AGNRs, finding significant differences versus the single-pz Model. These results show that an accurate bandstructure Model is essential for predicting the performance of graphene-based nanodevices.
V N Popov - One of the best experts on this subject based on the ideXlab platform.
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resonant raman intensity of the radial breathing mode of single walled carbon nanotubes within a nonorthogonal Tight Binding Model
Nano Letters, 2004Co-Authors: V N Popov, Luc Henrard, Philippe LambinAbstract:The resonant Raman intensity of the radial breathing mode is calculated for 50 narrow semiconducting single-walled carbon nanotubes within a symmetry-adapted nonorthogonal Tight-Binding Model. The matrix elements of the momentum and the deformation potential in the quantum-mechanical formula for the intensity are calculated explicitly. The results for the resonance Raman profiles can be used directly in the determination of the diameter distribution of the nanotubes in a sample. Three Raman spectra are simulated and compared to existing experimental data.
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curvature effects on the structural electronic and optical properties of isolated single walled carbon nanotubes within a symmetry adapted non orthogonal Tight Binding Model
New Journal of Physics, 2004Co-Authors: V N PopovAbstract:The effects of curvature on the structure, electronic and optical properties of isolated single-walled carbon nanotubes are studied within a symmetry-adapted non-orthogonal Tight-Binding Model using 2s and 2p electrons of carbon. The symmetry-adapted scheme allows reducing the matrix eigenvalue problem for the electrons to diagonalization of 8×8 matrices for any nanotube type. Due to this simplification, the electronic band structure of nanotubes with a very large number of atoms in the unit cell can be calculated. Using this Model, the structure of 187 small- and moderate-radius nanotubes is optimized. It is found that the deviations of the optimized structure from the non-optimized one are large for tube radii smaller than 5 A. The band structure and the dielectric function of 101 small- and moderate-radius nanotubes are calculated. The optical transition energies for these nanotubes are derived from the dielectric function and plotted versus tube radius. It is shown that the structural optimization introduces small changes to the transition energies obtained within the non-orthogonal Tight-Binding Model. The transition energies for the optimized structure within this Model agree well with the available ab initio data for a few nanotube types. On the other hand, the results for the former deviate widely from those used for nanotube characterization in π-band Tight-Binding Model especially for small-radius tubes. The derived transition energies can be used for the assignment of nanotube absorption spectra and for the selection of nanotube types for which the Raman scattering is resonant.
Che Ting Chan - One of the best experts on this subject based on the ideXlab platform.
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environment dependent Tight Binding potential Model
Physical Review B, 1996Co-Authors: Mingsheng Tang, Caizhuang Wang, Che Ting ChanAbstract:We present a Tight-Binding Model which goes beyond the traditional two-center approximation and allows the hopping parameters and the repulsive energy to be dependent on the Binding environment. Using carbon as an example, we show that the approach improves remarkably the transferability of the Tight-Binding Model. The properties of the higher-coordinated metallic structures are well described by the Model in addition to those of the lower-coordinated covalent structures. \textcopyright{} 1996 The American Physical Society.
Saroj K Nayak - One of the best experts on this subject based on the ideXlab platform.
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accurate six band nearest neighbor Tight Binding Model for the π bands of bulk graphene and graphene nanoribbons
Journal of Applied Physics, 2011Co-Authors: Timothy B Boykin, Gerhard Klimeck, Mathieu Luisier, Xueping Jiang, Neerav Kharche, Yu Zhou, Saroj K NayakAbstract:Accurate Modeling of the π-bands of armchair graphene nanoribbons (AGNRs) requires correctly reproducing asymmetries in the bulk graphene bands, as well as providing a realistic Model for hydrogen passivation of the edge atoms. The commonly used single-pz orbital approach fails on both these counts. To overcome these failures we introduce a nearest-neighbor, three orbital per atom p/d Tight-Binding Model for graphene. The parameters of the Model are fit to first-principles density-functional theory –based calculations as well as to those based on the many-body Green’s function and screened-exchange formalism, giving excellent agreement with the ab initio AGNR bands. We employ this Model to calculate the current-voltage characteristics of an AGNR MOSFET and the conductance of rough-edge AGNRs, finding significant differences versus the single-pz Model. These results show that an accurate band structure Model is essential for predicting the performance of graphene-based nanodevices.
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accurate six band nearest neighbor Tight Binding Model for the pi bands of bulk graphene and graphene nanoribbons
arXiv: Mesoscale and Nanoscale Physics, 2011Co-Authors: Timothy B Boykin, Gerhard Klimeck, Mathieu Luisier, Xueping Jiang, Neerav Kharche, Yu Zhou, Saroj K NayakAbstract:Accurate Modeling of the pi-bands of armchair graphene nanoribbons (AGNRs) requires correctly reproducing asymmetries in the bulk graphene bands as well as providing a realistic Model for hydrogen passivation of the edge atoms. The commonly used single-pz orbital approach fails on both these counts. To overcome these failures we introduce a nearest-neighbor, three orbital per atom p/d Tight-Binding Model for graphene. The parameters of the Model are fit to first-principles density-functional theory (DFT) - based calculations as well as to those based on the many-body Green's function and screened-exchange (GW) formalism, giving excellent agreement with the ab initio AGNR bands. We employ this Model to calculate the current-voltage characteristics of an AGNR MOSFET and the conductance of rough-edge AGNRs, finding significant differences versus the single-pz Model. These results show that an accurate bandstructure Model is essential for predicting the performance of graphene-based nanodevices.