Pub Date : 2009-05-27DOI: 10.1109/IWCE.2009.5091160
E. Ramayya, I. Knezevic
The room-temperature thermoelectric figure of merit (ZT) of highly doped silicon nanowires (SiNWs) of square cross section was calculated by solving the electron and phonon Boltzmann transport equations with a proper account of the two dimensional confinement of both electrons and phonons. The ZT in SiNWs is almost two orders of magnitude larger than that of bulk silicon. The enhancement of ZT in SiNWs occurs primarily because of strong phonon-boundary scattering that degrades the lattice thermal conductivity by about two orders of magnitude from its value in bulk silicon. With decreasing wire cross section, the electrical conductivity (sigma) and thermal conductivity (k) decrease, whereas the Seebeck coefficient (S) increases. Therefore, the ZT variation with cross section is nonmonotonic, with ZT maximal for a wire of cross section 4 times 4 nm 2 . Boundary roughness scattering indeed proves to have a significant effect on both electronic and thermal transport in SiNWs.
{"title":"Ultrascaled Silicon Nanowires as Efficient Thermoelectric Materials","authors":"E. Ramayya, I. Knezevic","doi":"10.1109/IWCE.2009.5091160","DOIUrl":"https://doi.org/10.1109/IWCE.2009.5091160","url":null,"abstract":"The room-temperature thermoelectric figure of merit (ZT) of highly doped silicon nanowires (SiNWs) of square cross section was calculated by solving the electron and phonon Boltzmann transport equations with a proper account of the two dimensional confinement of both electrons and phonons. The ZT in SiNWs is almost two orders of magnitude larger than that of bulk silicon. The enhancement of ZT in SiNWs occurs primarily because of strong phonon-boundary scattering that degrades the lattice thermal conductivity by about two orders of magnitude from its value in bulk silicon. With decreasing wire cross section, the electrical conductivity (sigma) and thermal conductivity (k) decrease, whereas the Seebeck coefficient (S) increases. Therefore, the ZT variation with cross section is nonmonotonic, with ZT maximal for a wire of cross section 4 times 4 nm 2 . Boundary roughness scattering indeed proves to have a significant effect on both electronic and thermal transport in SiNWs.","PeriodicalId":443119,"journal":{"name":"2009 13th International Workshop on Computational Electronics","volume":"65 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124936053","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2009-05-27DOI: 10.1109/IWCE.2009.5091156
S. Tyaginov, V. Sverdlov, W. Gos, T. Grasser
The McPherson model for the Si-O bond-breakage has been extended in a manner to capture the effect of O-Si-O angle variations on the breakage rate. Using a distribution function of the O-Si-O bond angle, a series of breakage rate probability densities has been calculated as a function of the applied electric field. Using such a distribution function we have calculated the mean vale and the standard deviation of the breakage rate and compare them to the nominal rate corresponding to the fixed angle of 109.48deg observed in crystalline alpha-quartz. It is shown that the mean value of this rate is substantially higher than and the standard deviation is comparable with the nominal rate. Obtained dependencies demonstrate a linear trend in a log-fin space, thereby validating the thermo-chemical model for the time-dependent-dielectric breakdown also in the case of non-uniform O-Si-O angle distribution typical for amorphous silica.
{"title":"Statistics of Si-O Bond-Breakage Rate Variations Induced by O-Si-O Angle Fluctuations","authors":"S. Tyaginov, V. Sverdlov, W. Gos, T. Grasser","doi":"10.1109/IWCE.2009.5091156","DOIUrl":"https://doi.org/10.1109/IWCE.2009.5091156","url":null,"abstract":"The McPherson model for the Si-O bond-breakage has been extended in a manner to capture the effect of O-Si-O angle variations on the breakage rate. Using a distribution function of the O-Si-O bond angle, a series of breakage rate probability densities has been calculated as a function of the applied electric field. Using such a distribution function we have calculated the mean vale and the standard deviation of the breakage rate and compare them to the nominal rate corresponding to the fixed angle of 109.48deg observed in crystalline alpha-quartz. It is shown that the mean value of this rate is substantially higher than and the standard deviation is comparable with the nominal rate. Obtained dependencies demonstrate a linear trend in a log-fin space, thereby validating the thermo-chemical model for the time-dependent-dielectric breakdown also in the case of non-uniform O-Si-O angle distribution typical for amorphous silica.","PeriodicalId":443119,"journal":{"name":"2009 13th International Workshop on Computational Electronics","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126814130","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2009-05-27DOI: 10.1109/IWCE.2009.5091082
H. Ryu, Sunhee Lee, Gerhard Klimeck
A highly phosphorus delta-doped Si device is modeled with a quantum well with periodic boundary conditions and the semi-empirical spds* tight-binding band model. Its temperature-dependent electronic properties are studied. To account for high doping density with many electrons, a highly parallelized self-consistent Schrodinger-Poisson solver is used with atomistic representations of multiple impurity ions. The band-structure in equilibrium and the corresponding Fermi-level position are computed for a selective set of temperatures. The result at room temperature is compared with previous studies and the temperature-dependent electronic properties are discussed further in detail with the calculated 3-D self-consistent potential profile.
{"title":"A Study of Temperature-dependent Properties of N-type d-doped Si Band-structures in Equilibrium","authors":"H. Ryu, Sunhee Lee, Gerhard Klimeck","doi":"10.1109/IWCE.2009.5091082","DOIUrl":"https://doi.org/10.1109/IWCE.2009.5091082","url":null,"abstract":"A highly phosphorus delta-doped Si device is modeled with a quantum well with periodic boundary conditions and the semi-empirical spds* tight-binding band model. Its temperature-dependent electronic properties are studied. To account for high doping density with many electrons, a highly parallelized self-consistent Schrodinger-Poisson solver is used with atomistic representations of multiple impurity ions. The band-structure in equilibrium and the corresponding Fermi-level position are computed for a selective set of temperatures. The result at room temperature is compared with previous studies and the temperature-dependent electronic properties are discussed further in detail with the calculated 3-D self-consistent potential profile.","PeriodicalId":443119,"journal":{"name":"2009 13th International Workshop on Computational Electronics","volume":"93 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127855034","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2009-05-27DOI: 10.1109/IWCE.2009.5091157
D. Fu, Rong Zhang, B. Liu, Z. Xie, X. Xiu, Hai Lu, Youdou Zheng, G. Edwards
In this paper, the k- p perturbation theory is adopted to calculate the interband excitonic transition energies and their polarization selection rules in c-plane A1N films, Ga x Al 1-x N and In x Al 1-x N alloys modulated by both isotropic biaxial in-plane strain and alloy compositions. It is shown that valence band mixing induced by both strain and alloy composition has dramatic influence on the optical polarization properties. The calculated results provide both good physical insight into the band structure engineering and helpful instructions in the future design of high efficient and novel UV-emitters.
本文采用k- p摄动理论计算了各向同性双轴面内应变和合金成分调制的c面A1N薄膜、Ga x Al 1-x N和In x Al 1-x N合金带间激子跃迁能及其极化选择规律。结果表明，由应变和合金成分引起的价带混合对光学偏振性能有显著影响。计算结果为波段结构工程提供了良好的物理见解，并为今后设计高效新型紫外发射体提供了有益的指导。
{"title":"Strain- and Compositional Modulation of the Near-Band-Edge Band Structures of AlN and Its Ternary Alloys with GaN and InN","authors":"D. Fu, Rong Zhang, B. Liu, Z. Xie, X. Xiu, Hai Lu, Youdou Zheng, G. Edwards","doi":"10.1109/IWCE.2009.5091157","DOIUrl":"https://doi.org/10.1109/IWCE.2009.5091157","url":null,"abstract":"In this paper, the k- p perturbation theory is adopted to calculate the interband excitonic transition energies and their polarization selection rules in c-plane A1N films, Ga x Al 1-x N and In x Al 1-x N alloys modulated by both isotropic biaxial in-plane strain and alloy compositions. It is shown that valence band mixing induced by both strain and alloy composition has dramatic influence on the optical polarization properties. The calculated results provide both good physical insight into the band structure engineering and helpful instructions in the future design of high efficient and novel UV-emitters.","PeriodicalId":443119,"journal":{"name":"2009 13th International Workshop on Computational Electronics","volume":"71 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121392222","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2009-05-27DOI: 10.1109/IWCE.2009.5091149
S. Souma, M. Ogawa, Takahiro Yamamoto, Kazuyuki Watanabe
We study the spin filtering characteristics of the zigzag-edged graphene nanoribbon spin filtering device, applying the spin-density functional tight-binding method and the non- equilibrium Green's function method. Our simulations have shown that the spin filtering effect can be controlled by applying the side-gate voltages that effectively induce the transverse electric fields. Influence of an edge lattice vacancy on the spin- filtering effect is also discussed.
{"title":"Simulation of Graphene Nanoribbon Spin-Filter Device with Spin-Density Functional Tight-Binding Method","authors":"S. Souma, M. Ogawa, Takahiro Yamamoto, Kazuyuki Watanabe","doi":"10.1109/IWCE.2009.5091149","DOIUrl":"https://doi.org/10.1109/IWCE.2009.5091149","url":null,"abstract":"We study the spin filtering characteristics of the zigzag-edged graphene nanoribbon spin filtering device, applying the spin-density functional tight-binding method and the non- equilibrium Green's function method. Our simulations have shown that the spin filtering effect can be controlled by applying the side-gate voltages that effectively induce the transverse electric fields. Influence of an edge lattice vacancy on the spin- filtering effect is also discussed.","PeriodicalId":443119,"journal":{"name":"2009 13th International Workshop on Computational Electronics","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125979029","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2009-05-27DOI: 10.1109/IWCE.2009.5091116
M. Bescond, M. Lannoo, L. Raymond, F. Michelini, M. Pala
This study presents ionized impurity impacts on silicon nanowire MOS transistors. We first calculate the current characteristics with a self-consistent three-dimensional (3D) Green's function approach and show the effects of both acceptor and donor impurities on the physical electron properties. In particular, we emphasize that the presence of a donor induces different transport phenomena according to the applied gate bias. Considering an attractive Coulomb potential, we then evaluate the effective mass validity by comparing the localized states of cubic dots with those obtained through a sp 3 third-neighbor tight-binding model. Our results show that in first approximation, the effective mass is still adapted to treat ionized impurities.
{"title":"Influence of Ionized Impurities in Silicon Nanowire MOS Transistors","authors":"M. Bescond, M. Lannoo, L. Raymond, F. Michelini, M. Pala","doi":"10.1109/IWCE.2009.5091116","DOIUrl":"https://doi.org/10.1109/IWCE.2009.5091116","url":null,"abstract":"This study presents ionized impurity impacts on silicon nanowire MOS transistors. We first calculate the current characteristics with a self-consistent three-dimensional (3D) Green's function approach and show the effects of both acceptor and donor impurities on the physical electron properties. In particular, we emphasize that the presence of a donor induces different transport phenomena according to the applied gate bias. Considering an attractive Coulomb potential, we then evaluate the effective mass validity by comparing the localized states of cubic dots with those obtained through a sp 3 third-neighbor tight-binding model. Our results show that in first approximation, the effective mass is still adapted to treat ionized impurities.","PeriodicalId":443119,"journal":{"name":"2009 13th International Workshop on Computational Electronics","volume":"06 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128241384","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2009-05-27DOI: 10.1109/IWCE.2009.5091140
M. Usman, H. Ryu, Sunhee Lee, Y. H. Tan, Gerhard Klimeck
The atomistic tight binding simulator NEMO 3-D has previously been validated against the experimental data for quantum dots, wells, and wires in the InGaAlAs and SiGe material systems. Here, we demonstrate our new capability to compute optical matrix elements and transition strengths in tight binding. Systematic multi-million atom electronic structure calculations explore the quantum confined stark shift and the ground state optical transition rate for an electric field in the lateral (100) direction. The simulations treat the strain in a ~15 million atom system and the electronic structure in a subset of ~9 million atoms. The effects of the long range strain, the optical polarization anisotropy, the interface roughness, and the non- degeneracy of the p-states which are missing in continuum methods like effective mass approximation or kp are included. A significant red shift in the emission spectra due to an applied in- plane electric field indicating a strong quantum confined stark effect (QSCE) is observed. The ground state optical transition rate rapidly decreases with the increasing electric field magnitude due to reduced spatial overlap of ground electron and hole states.
{"title":"Quantum Confined Stark Shift and Ground State Optical Transition Rate in [100] Laterally Biased InAs/GaAs Quantum Dots","authors":"M. Usman, H. Ryu, Sunhee Lee, Y. H. Tan, Gerhard Klimeck","doi":"10.1109/IWCE.2009.5091140","DOIUrl":"https://doi.org/10.1109/IWCE.2009.5091140","url":null,"abstract":"The atomistic tight binding simulator NEMO 3-D has previously been validated against the experimental data for quantum dots, wells, and wires in the InGaAlAs and SiGe material systems. Here, we demonstrate our new capability to compute optical matrix elements and transition strengths in tight binding. Systematic multi-million atom electronic structure calculations explore the quantum confined stark shift and the ground state optical transition rate for an electric field in the lateral (100) direction. The simulations treat the strain in a ~15 million atom system and the electronic structure in a subset of ~9 million atoms. The effects of the long range strain, the optical polarization anisotropy, the interface roughness, and the non- degeneracy of the p-states which are missing in continuum methods like effective mass approximation or kp are included. A significant red shift in the emission spectra due to an applied in- plane electric field indicating a strong quantum confined stark effect (QSCE) is observed. The ground state optical transition rate rapidly decreases with the increasing electric field magnitude due to reduced spatial overlap of ground electron and hole states.","PeriodicalId":443119,"journal":{"name":"2009 13th International Workshop on Computational Electronics","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130374232","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2009-05-27DOI: 10.1109/IWCE.2009.5091127
M. Shin
We have developed a full quantum transport simulator for nanowire field effect transistors based on the eight- band k ldr p Hamiltonian. The NEGF formalism was employed for transport calculation and the self-consistent calculations were performed. We were able to reduce the size of the Hamiltonian greatly by performing the mode-space transformation followed by selecting a small number of modes contributing to the transport. This, together with the approximate but highly accurate solutions of cross-section wave-functions, enabled us to carry out the transport calculation very efficiently. In this work, we demonstrate the capability of our simulator by showing the hole transport in PMOS Si nanowire transistors and the band-to-band tunneling in InAs nanowire transistors.
{"title":"NEGF Simulation of Nanowire Field Effect Transistors Using the Eight-band k · p method","authors":"M. Shin","doi":"10.1109/IWCE.2009.5091127","DOIUrl":"https://doi.org/10.1109/IWCE.2009.5091127","url":null,"abstract":"We have developed a full quantum transport simulator for nanowire field effect transistors based on the eight- band k ldr p Hamiltonian. The NEGF formalism was employed for transport calculation and the self-consistent calculations were performed. We were able to reduce the size of the Hamiltonian greatly by performing the mode-space transformation followed by selecting a small number of modes contributing to the transport. This, together with the approximate but highly accurate solutions of cross-section wave-functions, enabled us to carry out the transport calculation very efficiently. In this work, we demonstrate the capability of our simulator by showing the hole transport in PMOS Si nanowire transistors and the band-to-band tunneling in InAs nanowire transistors.","PeriodicalId":443119,"journal":{"name":"2009 13th International Workshop on Computational Electronics","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131017015","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2009-05-27DOI: 10.1109/IWCE.2009.5091083
Gerhard Klimeck, D. Vasileska
← ← Abstract — The ABACUS and AQME on-line tools and their associated wiki pages form one-stop shops for educators and students of existing university courses. They are geared towards courses like "introduction to Semiconductor Devices" and "Quantum Mechanics for Engineers". The service is free to anyone and no software installation is required on the user's computer. All simulations, including advanced visualization are performed at a remote computer. The tools have been deployed on nanoHUB.org in August 2008 and haven already been used by over 700 users. This paper describes nanoHUB educational tool user requirements and the motivation for and some details about these new tools. Usage patterns and future planned assessment are discussed. The concepts of "NCN supported" and "Community Supported" tools are discussed.
{"title":"ABACUS and AQME: Semiconductor Device and Quantum Mechanics Education on nanoHUB.org","authors":"Gerhard Klimeck, D. Vasileska","doi":"10.1109/IWCE.2009.5091083","DOIUrl":"https://doi.org/10.1109/IWCE.2009.5091083","url":null,"abstract":"← ← Abstract — The ABACUS and AQME on-line tools and their associated wiki pages form one-stop shops for educators and students of existing university courses. They are geared towards courses like \"introduction to Semiconductor Devices\" and \"Quantum Mechanics for Engineers\". The service is free to anyone and no software installation is required on the user's computer. All simulations, including advanced visualization are performed at a remote computer. The tools have been deployed on nanoHUB.org in August 2008 and haven already been used by over 700 users. This paper describes nanoHUB educational tool user requirements and the motivation for and some details about these new tools. Usage patterns and future planned assessment are discussed. The concepts of \"NCN supported\" and \"Community Supported\" tools are discussed.","PeriodicalId":443119,"journal":{"name":"2009 13th International Workshop on Computational Electronics","volume":"41 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133307887","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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