Bandstructure and effective mass

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• From http://www.intel.com/technology/mooreslaw/index.htm

Bandstructure and effective mass

• Bandstructure and effective mass

• Carrier confinement
• Atomic scale material variations
• Local strain variations
• Atomistic treatment of electric and magnetic fields

Valley-splitting

• Valley-splitting

• Highly dependent on atomic scale thickness variations
• Need atomistic modeling technique such as tight-binding

Motivation

• Motivation

• Tight-Binding Approach to Model Atomic Scale Variations

• Summary of Results

• Valley Degeneracies in (111) Si Quantum Wells
• Valley-Splitting in (100) SiGe/Si/SiGe Quantum Wells
• Transport Characteristics of AlGaAs Nanowires
• Ultra-Scaled InAs HEMTs

• Performance Analysis of Ultra-Scaled InAs HEMTs

• Modeling Approach
• Comparison to Experiments
• Scaling Considerations

• Summary of Contributions

• Outlook

Motivation

• Motivation

• Tight-Binding Approach to Model Atomic Scale Variations

• Summary of Results

• Valley Degeneracies in (111) Si Quantum Wells
• Valley-Splitting in (100) SiGe/Si/SiGe Quantum Wells
• Transport Characteristics of AlGaAs Nanowires
• Ultra-Scaled InAs HEMTs

• Performance Analysis of Ultra-Scaled InAs HEMTs

• Modeling Approach
• Comparison to Experiments
• Scaling Considerations

• Summary of Contributions

• Outlook

Objective

• Objective

• Resolve discrepancies in experimentally observed and theoretically predicted valley degeneracies

• Effect of surface miscut on the electronic structure

• Approach

• Supercell tight-binding approach to model surface miscuts

• Effective mass based valley-projection model to determine the directions of valley-minima of large supercells

• Insight

• Atomistic basis representation is essential to capture the effect of mono-atomic steps resulting from miscut

Motivation

• Motivation

• Tight-Binding Approach to Model Atomic Scale Variations

• Summary of Results

• Valley Degeneracies in (111) Si Quantum Wells
• Valley-Splitting in (100) SiGe/Si/SiGe Quantum Wells
• Transport Characteristics of AlGaAs Nanowires
• Ultra-Scaled InAs HEMTs

• Performance Analysis of Ultra-Scaled InAs HEMTs

• Modeling Approach
• Comparison to Experiments
• Scaling Considerations

• Summary of Contributions

• Outlook

Motivation

• Motivation

• Tight-Binding Approach to Model Atomic Scale Variations

• Summary of Results

• Valley Degeneracies in (111) Si Quantum Wells
• Valley-Splitting in (100) SiGe/Si/SiGe Quantum Wells
• Transport Characteristics of InAlAs Nanowires
• Ultra-Scaled InAs HEMTs

• Performance Analysis of Ultra-Scaled InAs HEMTs

• Modeling Approach
• Comparison to Experiments
• Scaling Considerations

• Summary of Contributions

• Outlook

Objective

• Objective

• Method to model bandstructure of disordered nanowires
• Detailed understanding of transport by comparing bandstructure and transmission characteristics

• Approach

• Transmission: Non-equilibrium Green’s function method
• Bandstructure: Supercell calculation and zone-unfolding

Motivation

• Motivation

• Tight-Binding Approach to Model Atomic Scale Variations

• Summary of Results

• Valley Degeneracies in (111) Si Quantum Wells
• Valley-Splitting in (100) SiGe/Si/SiGe Quantum Wells
• Transport Characteristics of InAlAs Nanowires
• Ultra-Scaled InAs HEMTs

• Performance Analysis of Ultra-Scaled InAs HEMTs

• Modeling Approach
• Comparison to Experiments
• Scaling Considerations

• Summary of Contributions

• Outlook

Objective

• Objective

• Develop: a methodology to simulate ultra-scaled InAs FETs
• Benchmark: match experimental I-Vs for “large” devices Lg = 30 - 50nm
• Improve: device design for scaling down to 20nm node

• Results/Impact

• Good quantitative match to experiments
• Performance optimization of 20nm device

Motivation

• Motivation

• Tight-Binding Approach to Model Atomic Scale Variations

• Summary of Results

• Valley Degeneracies in (111) Si Quantum Wells
• Valley-Splitting in (100) SiGe/Si/SiGe Quantum Wells
• Transport Characteristics of InAlAs Nanowires
• Ultra-Scaled InAs HEMTs

• Performance Analysis of Ultra-Scaled InAs HEMTs

• Modeling Approach
• Comparison to Experiments
• Scaling Considerations

• Summary of Contributions

• Outlook

III-V: Extraordinary electron transport properties and high injection velocities

• III-V: Extraordinary electron transport properties and high injection velocities

• HEMTs: Very similar structure to MOSFETs except high-κ dielectric layer

• Excellent to Test Performances of III-V material without interface defects

• Every Year Devices with a Shorter Gate Length Introduced by del Alamo’s Group at MIT

• Excellent to Test Simulation Models

• Develop simulation tools and benchmark with experiments
• Predict performance of ultra-scaled devices

Motivation

• Motivation

• Tight-Binding Approach to Model Atomic Scale Variations

• Summary of Results

• Valley Degeneracies in (111) Si Quantum Wells
• Valley-Splitting in (100) SiGe/Si/SiGe Quantum Wells
• Transport Characteristics of InAlAs Nanowires
• Ultra-Scaled InAs HEMTs

• Performance Analysis of Ultra-Scaled InAs HEMTs

• Modeling Approach
• Comparison to Experiments
• Scaling Considerations

• Summary of Contributions

• Outlook

Intrinsic device

• Intrinsic device

• Near gate contact
• Self consistent 2D Schrodinger-Poisson
• Electrons injected from all contacts

• Extrinsic source/drain contacts

• Series resistances RS and RD

Motivation

• Motivation

• Tight-Binding Approach to Model Atomic Scale Variations

• Summary of Results

• Valley Degeneracies in (111) Si Quantum Wells
• Valley-Splitting in (100) SiGe/Si/SiGe Quantum Wells
• Transport Characteristics of InAlAs Nanowires
• Ultra-Scaled InAs HEMTs

• Performance Analysis of Ultra-Scaled InAs HEMTs

• Modeling Approach
• Comparison to Experiments
• Scaling Considerations

• Summary of Contributions

• Outlook

Motivation

• Motivation

• Tight-Binding Approach to Model Atomic Scale Variations

• Summary of Results

• Valley Degeneracies in (111) Si Quantum Wells
• Valley-Splitting in (100) SiGe/Si/SiGe Quantum Wells
• Transport Characteristics of InAlAs Nanowires
• Ultra-Scaled InAs HEMTs

• Performance Analysis of Ultra-Scaled InAs HEMTs

• Modeling Approach
• Comparison to Experiments
• Scaling Considerations

• Summary of Contributions

• Outlook

Motivation

• Motivation

• Tight-Binding Approach to Model Atomic Scale Variations

• Summary of Results

• Valley Degeneracies in (111) Si Quantum Wells
• Valley-Splitting in (100) SiGe/Si/SiGe Quantum Wells
• Transport Characteristics of InAlAs Nanowires
• Ultra-Scaled InAs HEMTs

• Performance Analysis of Ultra-Scaled InAs HEMTs

• Modeling Approach
• Comparison to Experiments
• Scaling Considerations

• Summary of Contributions

• Outlook

(111) Si quantum wells: Explained 2-4 valley degeneracy breaking (APL 2009)

• (111) Si quantum wells: Explained 2-4 valley degeneracy breaking (APL 2009)

• Miscut (100) SiGe/Si/SiGe quantum wells: Provided qualitative and quantitative understanding of valley splitting (APL 2007)

AlGaAs and SiGe nanowires: Provided understanding of transmission coefficients by employing zone-unfolding method (TNANO 2007, JCE 07)

• AlGaAs and SiGe nanowires: Provided understanding of transmission coefficients by employing zone-unfolding method (TNANO 2007, JCE 07)

• InAs HEMTs: Demonstrated quantitative agreement between experiments and simulations. Performance optimizations for ultra-scaled HEMTs (IEDM 09)

Motivation

• Motivation

• Tight-Binding Approach to Model Atomic Scale Variations

• Summary of Results

• Valley Degeneracies in (111) Si Quantum Wells
• Valley-Splitting in (100) SiGe/Si/SiGe Quantum Wells
• Transport Characteristics of InAlAs Nanowires
• Ultra-Scaled InAs HEMTs

• Performance Analysis of Ultra-Scaled InAs HEMTs

• Modeling Approach
• Comparison to Experiments
• Scaling Considerations

• Summary of Contributions

• Outlook

Valley degeneracies in (110) Si QWs

• Valley degeneracies in (110) Si QWs

• Both 4 and 2 fold valley degeneracies are reported in experiments
• Flat (110) => 2 fold degenerate
• Miscut (110) => 4 fold degenerate

• Effect of Ge concentration on valley splitting in (100) SiGe/Si/SiGe QWs

• Disorder in SiGe reduces valley splitting and sensitivity to Ge concentration

Supercell approach and zone-unfolding

• Supercell approach and zone-unfolding

• Electronic structure of rough nanowires and QWs
• Hole transport in SiGe pMOS devices

• III-V MOSFETs

Advisors:

• Advisors:

• Professor Gerhard Klimeck
• Professor Timothy Boykin

• Committee members:

• Professor Mark Lundstrom
• Professor Supriyo Datta
• Professor Ronald Reifenberger

• Dr. Mathieu Luisier

• Klimeck Group Members and Labmates

InAs Channel Scaling:

• InAs Channel Scaling:

• Better electrostatic control

• lower SS
• larger ION/IOFF ratio

• Increase of transport m*

• reduced vinj, higher Ninv => higher ION

• Increase of gate leakage current

• ION/IOFF ratio saturates

InAlAs Insulator Scaling:

• InAlAs Insulator Scaling:

• Better electrostatic control (due to larger Cox)

• Increase of gate leakage current

• larger IOFF
• larger SS
• smaller ION/IOFF ratio

Electrons tunnel from gate into InAs channel

• Electrons tunnel from gate into InAs channel

• Tunneling barriers

• InAlAs and InGaAs
• Position dependent barriers

• Current crowding at edges (due to lower tunneling barriers)

• Barriers modulated by ΦM

Characteristics:

• Characteristics:

• Same Gate Overdrive

• same thermionic current (source to drain)

• Gate Fermi levels shifted by ΔΦM

• different tunneling barrier height

• ΦM =4.7 eV

• tunnel through InAlAs only
• larger Ig

• ΦM =5.1 eV

• tunnel through InAlAs and InGaAs
• lower Ig