Pub Date : 2015-09-01DOI: 10.1109/IWCE.2015.7301940
T. Ameen, H. Ilatikhameneh, Daniel Valencia, R. Rahman, Gerhard Klimeck
In this paper, we report a fast effective mass model for accurately calculating the bound states and optical transitions of self-assembled quantum dots. The model includes the atomistic strain effects, namely, the strain deformation of the band edges, and strain modification of the effective masses. The explicit inclusion of strain effects in the picture has significantly improved the effective mass model results. For strain calculations, we have found that atomistic strain depends solely on the aspect ratio of the quantum dot, and it has been calculated and reported here for a wide range of quantum dot aspect ratios. Following this sole dependence on the aspect ratio; The deformation theory has been used to include the strain deformation of the band edges. Density function theory has been used to study the effect of strain on the electron and hole effective masses. The proposed effective mass model have an accuracy that is close to full atomistic simulation but with no computational cost.
{"title":"Engineering the optical transitions of self-assembled quantum dots","authors":"T. Ameen, H. Ilatikhameneh, Daniel Valencia, R. Rahman, Gerhard Klimeck","doi":"10.1109/IWCE.2015.7301940","DOIUrl":"https://doi.org/10.1109/IWCE.2015.7301940","url":null,"abstract":"In this paper, we report a fast effective mass model for accurately calculating the bound states and optical transitions of self-assembled quantum dots. The model includes the atomistic strain effects, namely, the strain deformation of the band edges, and strain modification of the effective masses. The explicit inclusion of strain effects in the picture has significantly improved the effective mass model results. For strain calculations, we have found that atomistic strain depends solely on the aspect ratio of the quantum dot, and it has been calculated and reported here for a wide range of quantum dot aspect ratios. Following this sole dependence on the aspect ratio; The deformation theory has been used to include the strain deformation of the band edges. Density function theory has been used to study the effect of strain on the electron and hole effective masses. The proposed effective mass model have an accuracy that is close to full atomistic simulation but with no computational cost.","PeriodicalId":165023,"journal":{"name":"2015 International Workshop on Computational Electronics (IWCE)","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121509934","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 : 2015-09-01DOI: 10.1109/IWCE.2015.7301968
C. Jirauschek
A characteristic feature of the quantum cascade laser (QCL) is that the optical properties of the active region can be custom-tailored by quantum engineering. Recently, the possibility to integrate giant artificial optical nonlinearities has enabled various novel applications, such as room temperature terahertz generation based on difference frequency mixing and the QCL-based generation of mid-infrared and terahertz frequency combs. We extend established modeling approaches, such as the ensemble Monte Carlo method, to the simulation of such nonlinear optical QCL sources. The obtained theoretical results are shown to be consistent with available experimental data.
{"title":"Modeling of quantum cascade laser sources with giant optical nonlinearities","authors":"C. Jirauschek","doi":"10.1109/IWCE.2015.7301968","DOIUrl":"https://doi.org/10.1109/IWCE.2015.7301968","url":null,"abstract":"A characteristic feature of the quantum cascade laser (QCL) is that the optical properties of the active region can be custom-tailored by quantum engineering. Recently, the possibility to integrate giant artificial optical nonlinearities has enabled various novel applications, such as room temperature terahertz generation based on difference frequency mixing and the QCL-based generation of mid-infrared and terahertz frequency combs. We extend established modeling approaches, such as the ensemble Monte Carlo method, to the simulation of such nonlinear optical QCL sources. The obtained theoretical results are shown to be consistent with available experimental data.","PeriodicalId":165023,"journal":{"name":"2015 International Workshop on Computational Electronics (IWCE)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122708383","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 : 2015-09-01DOI: 10.1109/IWCE.2015.7301958
W. Frensley
The longstanding problem of spurious states in k·p models of semiconductor nanostructures has been shown to be an artifact of the use of the centereddifference approximation to the gradient, and it has been shown that stable models may be constructed on the basis of lower-order one-sided differences. The present paper demonstrates how the resulting bulk bandstructure models may be applied to heterostructures without introducing anomalies in the wavefunction behavior. This is done by constructing a variational functional in which the desired wavefunction continuity and boundary values are explicitly inserted, and then deriving the discrete Hamiltonian from that functional.
{"title":"Variational formulation of stable discrete k·p models","authors":"W. Frensley","doi":"10.1109/IWCE.2015.7301958","DOIUrl":"https://doi.org/10.1109/IWCE.2015.7301958","url":null,"abstract":"The longstanding problem of spurious states in k·p models of semiconductor nanostructures has been shown to be an artifact of the use of the centereddifference approximation to the gradient, and it has been shown that stable models may be constructed on the basis of lower-order one-sided differences. The present paper demonstrates how the resulting bulk bandstructure models may be applied to heterostructures without introducing anomalies in the wavefunction behavior. This is done by constructing a variational functional in which the desired wavefunction continuity and boundary values are explicitly inserted, and then deriving the discrete Hamiltonian from that functional.","PeriodicalId":165023,"journal":{"name":"2015 International Workshop on Computational Electronics (IWCE)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125922738","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 : 2015-09-01DOI: 10.1109/IWCE.2015.7301972
P. Marconcini, M. Macucci, E. Herbschleb, M. Connolly
We present numerical simulations that we have performed with the aim of interpreting the results of the transport measurements that we have recently obtained on a graphene device in which a cavity-shaped potential, orthogonal to the transport direction, had been induced with electrostatic lithography. The resistance of the sample has been computed for a broad spectrum of possible potential configurations, both as a function of the backgate voltage, and of the position of a biased probe scanned at a fixed distance from the graphene sheet. The comparison between the experimental measurements and the numerical results have allowed us to determine the details of the potential profile in the device.
{"title":"Simulation of transport through a cavity defined in graphene with electrostatic lithography","authors":"P. Marconcini, M. Macucci, E. Herbschleb, M. Connolly","doi":"10.1109/IWCE.2015.7301972","DOIUrl":"https://doi.org/10.1109/IWCE.2015.7301972","url":null,"abstract":"We present numerical simulations that we have performed with the aim of interpreting the results of the transport measurements that we have recently obtained on a graphene device in which a cavity-shaped potential, orthogonal to the transport direction, had been induced with electrostatic lithography. The resistance of the sample has been computed for a broad spectrum of possible potential configurations, both as a function of the backgate voltage, and of the position of a biased probe scanned at a fixed distance from the graphene sheet. The comparison between the experimental measurements and the numerical results have allowed us to determine the details of the potential profile in the device.","PeriodicalId":165023,"journal":{"name":"2015 International Workshop on Computational Electronics (IWCE)","volume":"94 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121339691","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 : 2015-09-01DOI: 10.1109/IWCE.2015.7301984
Jaime Bohórquez-Ballén, Hansika I. Sirikumara, Shaikh Ahmedy, T. Jayasekera
Using first principles Density Functional Theory (DFT) calculations, we have studied the structural and lattice vibrational properties of [111]-oriented Si/Ge core-shell nanowires. Our results show that the fundamental atomicity of the underlying lattice is important for an accurate explanation of phonon frequencies. The detailed analysis shows that thermal conductance due to selective phonon modes of Si/Ge coreshell nanowires can be suppressed by engineering the ratio of core/shell atoms, as well as the detailed atomistic configuration. In particular, our results reveal that heavier shell atoms in Si/Ge core-shell nanowires reduce thermal conductivity, increasing their thermoelectric figure of merit.
{"title":"Lattice vibrational properties of Si/Ge core-shell nanowires for thermoelectric applications","authors":"Jaime Bohórquez-Ballén, Hansika I. Sirikumara, Shaikh Ahmedy, T. Jayasekera","doi":"10.1109/IWCE.2015.7301984","DOIUrl":"https://doi.org/10.1109/IWCE.2015.7301984","url":null,"abstract":"Using first principles Density Functional Theory (DFT) calculations, we have studied the structural and lattice vibrational properties of [111]-oriented Si/Ge core-shell nanowires. Our results show that the fundamental atomicity of the underlying lattice is important for an accurate explanation of phonon frequencies. The detailed analysis shows that thermal conductance due to selective phonon modes of Si/Ge coreshell nanowires can be suppressed by engineering the ratio of core/shell atoms, as well as the detailed atomistic configuration. In particular, our results reveal that heavier shell atoms in Si/Ge core-shell nanowires reduce thermal conductivity, increasing their thermoelectric figure of merit.","PeriodicalId":165023,"journal":{"name":"2015 International Workshop on Computational Electronics (IWCE)","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126686274","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 : 2015-09-01DOI: 10.1109/IWCE.2015.7301967
J. Jerome
In a recent publication, the author has established the existence of a unique weak solution of the initial/boundaryvalue problem for a closed quantum system modeled by time dependent density function theory (TDDFT). We describe a Newton iteration, based upon the technique used to prove (unique) existence for the TDDFT model.We show that successive approximation at the operator level, based upon the evolution operator, is sufficient to obtain a `starting iterate' for Newton's method. We discuss the so-called quadratic convergence associated with Newton's method. In the process, we obtain a Kantorovich type theorem for TDDFT.
{"title":"Operator newton iterative convergence for time dependent density functional theory","authors":"J. Jerome","doi":"10.1109/IWCE.2015.7301967","DOIUrl":"https://doi.org/10.1109/IWCE.2015.7301967","url":null,"abstract":"In a recent publication, the author has established the existence of a unique weak solution of the initial/boundaryvalue problem for a closed quantum system modeled by time dependent density function theory (TDDFT). We describe a Newton iteration, based upon the technique used to prove (unique) existence for the TDDFT model.We show that successive approximation at the operator level, based upon the evolution operator, is sufficient to obtain a `starting iterate' for Newton's method. We discuss the so-called quadratic convergence associated with Newton's method. In the process, we obtain a Kantorovich type theorem for TDDFT.","PeriodicalId":165023,"journal":{"name":"2015 International Workshop on Computational Electronics (IWCE)","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131412782","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 : 2015-09-01DOI: 10.1109/IWCE.2015.7301974
A. Martinez, R. Valin, J. Barker
Non-equilibrium Green's Function simulations of an ultra-scale FinFET in the ballistic regime have been carried at low/high drain bias. We have calculated variability due to random dopants located in the source/drain regions of the transistor. The channel length of the scaled transistor is under 10 nm and therefore substantial tunnelling is expected. We have calculated the tunnelling as a function of the gate bias in two dopant configurations with the lowest and highest drain current. We have also computed the threshold voltage, sub-threshold slope and off current variability. We have studied the effect of the exchange correlation on the simulation of a cluster of dopants in the channel of the transistor.
{"title":"Impact of discrete dopants in ultra-scale finfets and the effect of XC on dopant clustering","authors":"A. Martinez, R. Valin, J. Barker","doi":"10.1109/IWCE.2015.7301974","DOIUrl":"https://doi.org/10.1109/IWCE.2015.7301974","url":null,"abstract":"Non-equilibrium Green's Function simulations of an ultra-scale FinFET in the ballistic regime have been carried at low/high drain bias. We have calculated variability due to random dopants located in the source/drain regions of the transistor. The channel length of the scaled transistor is under 10 nm and therefore substantial tunnelling is expected. We have calculated the tunnelling as a function of the gate bias in two dopant configurations with the lowest and highest drain current. We have also computed the threshold voltage, sub-threshold slope and off current variability. We have studied the effect of the exchange correlation on the simulation of a cluster of dopants in the channel of the transistor.","PeriodicalId":165023,"journal":{"name":"2015 International Workshop on Computational Electronics (IWCE)","volume":"290 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117050811","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 : 2015-09-01DOI: 10.1109/IWCE.2015.7301963
E. Hedin, M. Orvis, Y. S. Joe
Transmission properties of a linear chain of nanorings with 6 quantum dots (QD) per ring are investigated with and without magnetic field effects. The rings are connected serially by a linear segment. A tightbinding Hamiltonian is solved exactly, giving the transmission for any number of rings in series. The Aharonov-Bohm effect shifts and splits the transmission band structure and the Zeeman effect splits the transmission into spin-polarized bands. Multiple system parameters, including coupling integrals and ring number, are varied and shown to have significant effects on the transmission spectrum. The system and results provide generalized conduction properties of a 1-ring wide graphene nanoribbon in the armchair configuration.
{"title":"Coupled nano-rings: strain and magnetic field effects","authors":"E. Hedin, M. Orvis, Y. S. Joe","doi":"10.1109/IWCE.2015.7301963","DOIUrl":"https://doi.org/10.1109/IWCE.2015.7301963","url":null,"abstract":"Transmission properties of a linear chain of nanorings with 6 quantum dots (QD) per ring are investigated with and without magnetic field effects. The rings are connected serially by a linear segment. A tightbinding Hamiltonian is solved exactly, giving the transmission for any number of rings in series. The Aharonov-Bohm effect shifts and splits the transmission band structure and the Zeeman effect splits the transmission into spin-polarized bands. Multiple system parameters, including coupling integrals and ring number, are varied and shown to have significant effects on the transmission spectrum. The system and results provide generalized conduction properties of a 1-ring wide graphene nanoribbon in the armchair configuration.","PeriodicalId":165023,"journal":{"name":"2015 International Workshop on Computational Electronics (IWCE)","volume":"22 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133115443","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 : 2015-09-01DOI: 10.1109/IWCE.2015.7301985
Z. Stanojevic, M. Karner, F. Mitterbauer, C. Kernstock
A physically-grounded modeling, simulation, and parameter-extraction framework that targets design and engineering of ultra-scaled devices and next-generation channel materials. The framework consists of a fast and accurate Schrdinger-Poisson solver/mobility extractor coupled to a device simulator. It brings physical modeling of semiconductor channels to device design and engineering which until now has been the domain of TCAD tools based on purely empirical models. In this work, we specifically explore the framework components required to model devices based on III/V compound semiconductors.
{"title":"New computational perspectives on scattering and transport in III/V channel materials","authors":"Z. Stanojevic, M. Karner, F. Mitterbauer, C. Kernstock","doi":"10.1109/IWCE.2015.7301985","DOIUrl":"https://doi.org/10.1109/IWCE.2015.7301985","url":null,"abstract":"A physically-grounded modeling, simulation, and parameter-extraction framework that targets design and engineering of ultra-scaled devices and next-generation channel materials. The framework consists of a fast and accurate Schrdinger-Poisson solver/mobility extractor coupled to a device simulator. It brings physical modeling of semiconductor channels to device design and engineering which until now has been the domain of TCAD tools based on purely empirical models. In this work, we specifically explore the framework components required to model devices based on III/V compound semiconductors.","PeriodicalId":165023,"journal":{"name":"2015 International Workshop on Computational Electronics (IWCE)","volume":"192 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122432772","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 : 2015-09-01DOI: 10.1109/IWCE.2015.7301965
Jun Z. Huang, Kuang-Chung Wang, W. Frensley, Gerhard Klimeck
Multi-band k · p models discretized with finite difference method (FDM) have been widely used to study electronic properties of semiconductor nanostructures. However, different schemes of FDM exist in the literature, some of them are numerically unstable leading to spurious states [1][2], while others are stable but require special treatment of the boundary conditions and/or the material interfaces [3][4][5][6]. Therefore, a comparison of their numerical behaviors (and implementation tricks) will be very helpful for selecting a suitable scheme and obtaining reliable results. To this end, we have implemented into NEMO5 simulation software [7] the following options, (a) centered difference for symmetrized (SYM) Hamiltonian [1], (b) centered difference for Burt-Foreman (BF) Hamiltonian [8], (c) one-sided differences for SYM Hamiltonian [3], and (d) one-sided differences for BF Hamiltonian [6]. For all cases, eight-band and six-band models for both zincblende and wurtzite type materials are available.
{"title":"Finite difference schemes for k ⋅ p models: A comparative study","authors":"Jun Z. Huang, Kuang-Chung Wang, W. Frensley, Gerhard Klimeck","doi":"10.1109/IWCE.2015.7301965","DOIUrl":"https://doi.org/10.1109/IWCE.2015.7301965","url":null,"abstract":"Multi-band k · p models discretized with finite difference method (FDM) have been widely used to study electronic properties of semiconductor nanostructures. However, different schemes of FDM exist in the literature, some of them are numerically unstable leading to spurious states [1][2], while others are stable but require special treatment of the boundary conditions and/or the material interfaces [3][4][5][6]. Therefore, a comparison of their numerical behaviors (and implementation tricks) will be very helpful for selecting a suitable scheme and obtaining reliable results. To this end, we have implemented into NEMO5 simulation software [7] the following options, (a) centered difference for symmetrized (SYM) Hamiltonian [1], (b) centered difference for Burt-Foreman (BF) Hamiltonian [8], (c) one-sided differences for SYM Hamiltonian [3], and (d) one-sided differences for BF Hamiltonian [6]. For all cases, eight-band and six-band models for both zincblende and wurtzite type materials are available.","PeriodicalId":165023,"journal":{"name":"2015 International Workshop on Computational Electronics (IWCE)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131079109","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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