
Empirical Tightbinding Parameterization of SmSe in the sp3d5f7s* model
26 Mar 2013  Downloads  Contributor(s): Zhengping Jiang, Marcelo Kuroda, Yaohua Tan, Dennis M. Newns, Michael Povolotskyi, Timothy Boykin, Tillmann Christoph Kubis, Gerhard Klimeck, Glenn J. Martyna
The Empirical Tight Binding(ETB) method is widely used in atomistic device simulations. The reliability of such simulations depends very strongly on the choice of basis sets and the ETB parameters.
The Piezoelectronic Transistor (PET) has been proposed as a postCMOS device for fast, lowpower switching. In this device the piezoresistive channel is metalized via the expansion of a relaxor piezoelectric element. The mixedvalence compound SmSe is a good choice of PET channel material …

Tight Binding Parameters by DFT mapping
12 Sep 2012  Presentation Materials  Contributor(s): Yaohua Tan, Michael Povolotskyi, Tillmann Christoph Kubis, Yu He, Zhengping Jiang, Timothy Boykin, Gerhard Klimeck
The Empirical Tight Binding(ETB) method is widely used in atomistic device simulations. The reliability of such simulations depends very strongly on the choice of basis sets and the ETB parameters. The traditional way of obtaining the ETB parameters is by fitting to experiment data,or critical theoretical bandedges and symmetries rather than a foundational mapping. A further shortcoming of traditional ETB is the lack of an explicit basis. Alternatively, a DFT mapping process which constructs...

Nanoelectronic Modeling Lecture 35: Alloy Disorder in Nanowires
05 Aug 2010  Online Presentations  Contributor(s): Gerhard Klimeck, Timothy Boykin, Neerav Kharche, Mathieu Luisier, Neophytos Neophytou
This presentation discusses the consequences of Alloy Disorder in unstrained strained AlGaAs nanowires
 Relationship between dispersion relationship and transmission in perfectly ordered wires
 Band folding in Si nanowires
 Tranmisison in disordered wires – relationship to an approximate bandstructre
 Reminder of the origin of bandstructure and bandstructure engineering
 Localization of wavefunctions
Learning Objectives:
 Alloy wires are NOT smooth
 “Conduction band edge” flucatuates locally
 Dispersion changes
 Transmission and Density of states show localization effects

Nanoelectronic Modeling Lecture 34: Alloy Disorder in Quantum Dots
05 Aug 2010  Online Presentations  Contributor(s): Gerhard Klimeck, Timothy Boykin, Chris Bowen
This presentation discusses the consequences of Alloy Disorder in strained InGaAs Quantum Dots
 Reminder of the origin of bandstructure and bandstructure engineering
 What happens when there is disorder?
 Concept of disorder in the local bandstructure
 Configuration noise, concentration noise, clustering
Learning Objectives:
 Devicetodevice fluctuations in nanostructures may be significant even if the shape and size of the quantum dots remain perfectly controlled.
 Configuration noise, concentration noise and clustering in perfectly size and shape controlled quantum dots can lead to optical transition fluctuations that should be experimentally relevant.

Nanoelectronic Modeling Lecture 33: Alloy Disorder in Bulk
04 Aug 2010  Online Presentations  Contributor(s): Gerhard Klimeck, Timothy Boykin, Chris Bowen
This presentation discusses disorder in AlGaAs unstrained systems in bulk.
 Bandstructure of an ideal simple unit cell
 What happens when there is disorder?
 Concept of a supercell
 Band folding in a supercell
 Band extraction from the concept of approximate bandstructure
 Comparison of alloy disorder with the virtual crystal approximation
 Configuration noise, concentration noise
 How large does an alloy supercell have to be? When does the “bulk” condition occur?
Learning Objectives:
 Bandedges and bandgaps are influenced by:
 Placement / configuration disorder
 Concentration noise
 Clustering
 System size is very important
 “bulk” starts at 100,000 atoms
 => Nanostructures are not “bulk”
=> like quantum dots, nanowires, and quantum wells vary locally

Valley splitting in strained silicon quantum wells modeled with 2 degree miscuts, step disorder, and alloy disorder
14 Jan 2008  Papers  Contributor(s): Neerav Kharche, marta prada, Timothy Boykin, Gerhard Klimeck
Valley splitting (VS) in strained SiGe/Si/SiGe quantum wells grown on (001) and 2° miscut substrates is computed in a magnetic field. Calculations of flat structures significantly overestimate, while calculations of perfectly ordered structures underestimate experimentally observed VS. Step disorder and confinement alloy disorder raise the VS to the experimentally observed levels. Atomistic alloy disorder is identified as the critical physics, which cannot be modeled with analytical effective ...

Atomistic Simulation of Realistically Sized Nanodevices Using NEMO 3D—Part II: Applications
14 Jan 2008  Papers  Contributor(s): Gerhard Klimeck, Shaikh S. Ahmed, Neerav Kharche, Marek Korkusinski, Muhammad Usman, marta prada, Timothy Boykin
In part I, the development and deployment of a general nanoelectronic modeling tool (NEMO 3D) has been discussed. Based on the atomistic valenceforce field and the sp3d5s* nearest neighbor tightbinding models, NEMO 3D enables the computation of strain and electronic structure in nanostructures consisting of more than 64 and 52 million atoms, corresponding to volumes of (110 nm)3 and (101 nm)3, respectively. In this part, successful applications of NEMO 3D are demonstrated in the atomistic ...

Atomistic Simulation of Realistically Sized Nanodevices Using NEMO 3D: Part I − Models and Benchmarks
14 Jan 2008  Papers  Contributor(s): Gerhard Klimeck, Shaikh S. Ahmed, Neerav Kharche, Hansang Bae, Steven Clark, Benjamin P Haley, Maxim Naumov, Hoon Ryu, Faisal Saied, marta prada, Marek Korkusinski, Timothy Boykin
Device physics and material science meet at the atomic scale of novel nanostructured semiconductors, and the distinction between new device or new material is blurred. Not only the quantummechanical effects in the electronic states of the device but also the granular atomistic representation of the underlying material are important. Approaches based on a continuum representation of the underlying material typically used by device engineers and physicists become invalid. Ab initio methods used ...

Atomistic Electronic Structure Calculations of Unstrained Alloyed Systems Consisting of a Million Atoms
14 Jan 2008  Papers  Contributor(s): Gerhard Klimeck, Timothy Boykin
The broadening of the conduction and valence band edges due to compositional disorder in alloyed materials of finite extent is studied using an s p3 s ∗ tight binding model. Two sources of broadening due to configuration and concentration disorder are identified. The concentrational disorder dominates for systems up to at least one million atoms and depends on problem size through an inverse square root law. Significant differences (over 12 meV) in band edge energies are seen depending on ...

Development of a Nanoelectronic 3D (NEMO 3D ) Simulator for Multimillion Atom Simulations and Its Application to Alloyed Quantum Dots
14 Jan 2008  Papers  Contributor(s): Gerhard Klimeck, Timothy Boykin
Material layers with a thickness of a few nanometers are commonplace in today’s semiconductor
devices. Before long, device fabrication methods will reach a point at which the other two device
dimensions are scaled down to few tens of nanometers. The total atom count in such decanano
devices is reduced to a few million. Only a small finite number of “free” electrons will operate such
nanoscale devices due to quantized electron energies and electron charge. This work demonstrates
that ...