AP
Uploaded byAbhijeet Paul
PDF, PPTX541 views

PhD_10_2011_Abhijeet_Paul

This document provides an outline for a talk on electronic and thermal properties of semiconductor nanostructures from atomistic modeling and simulation. It motivates the importance of integrated atomistic simulation to study next-generation devices facing CMOS scaling challenges. It describes using an atomistic tight-binding approach and charge-potential self-consistent solution to model silicon nanowire field effect transistors, validated against experimental devices. The talk aims to discuss applications to silicon and gallium arsenide nanostructures and disseminating findings through nanohub.org.

Embed presentation

Download as PDF, PPTX
Network for Computational Nanotechnology (NCN)Purdue, Norfolk State, Northwestern, MIT, Molecular Foundry, UC Berkeley, Univ. of Illinois, UTEP Electronic and Thermal properties of  semiconductor nanostructures: A modeling and simulation study Abhijeet Paul Network for Computational Nanotechnology  (NCN), Electrical and Computer Engineering Purdue University email: abhijeet.rama@gmail.com 
Abhijeet Paul Acknowledgements • Overall guidance and direction » Prof. Gerhard Klimeck, Prof. Mark Lundstrom, Purdue University, USA. » Prof. Timothy Boykin, University of Alabama at Huntsville, USA (PhD committee member). » Prof. Leonid Rokhinson, Purdue University, USA (PhD committee member). • Theory and Code development » Dr. Mathieu Luisier, ETH Zurich, Switzerland (OMEN/OMEN-BSLAB development). » Prof. Timothy Boykin, University of Alabama Huntsville, USA (Tight-Binding and solid state phys. theory) » Dr. Neophytos Neophytou, TU Wien, Austria (Initial MATLAB codes) • Discussions and work » Saumitra Mehrotra, Parijat Sengupta, Shuaib Salamat, Sunhee Lee, Lang Zeng, Mehdi Salmani, Kai Miao, Dr. Raseong Kim and Changwook Jeong, Purdue University. • .Experimental Collaborators » Dr. Giuseppe Tettamanzi, TU Delft, Netherlands, Shweta Deora, IIT Bombay, India, Dr. Subash Rustagi, IME, Singapore, Dr. Mark Rodwell, UCSB, USA. • Summer Undergrad students (for nanohub tools) » Junzhe Geng, Victoria Savikhin, Mohammad Zulkifli, and Siqi Wang, Purdue University. • Funding and Computational Resources » MSD-FCRP, SRC, NSF and MIND for funding. » NCN and nanoHUB.org for computational resources. 2
Abhijeet Paul PhD timeline and progress [A] N. Singh et. al, EDL 2006 [B] A. Hochbaum et. al, Nature, 2008 [C] Yu et. al, Nature, 2010. [D] Pernot et. al, Nature, 2010. Important experimental works that guided this PhD work.Important experimental works that guided this PhD work. 3
Abhijeet Paul Outline of the talk • Motivation » Why the present work is important ? » Need for integrated atomistic simulation framework • Computational modeling and simulation approaches. • Application of the methods to Si nanowires (SiNWs). • Application to non-Si system  GaAs a quick look !! • Global dissemination of findings  nanoHUB.org • Summary • Future directions 4
Abhijeet Paul MoreMoore(MM)BeyondSi More than Moore(MtM)  Beyond CMOS 90 nm 90 nm 65 nm 65 nm 45 nm 45 nm 32 nm 32 nm 22 nm 22 nm BaselineCMOS:CPU,Memory,Logic Analog RF Analog RF SensorSensor Thermo electricity Thermo electricity Bio-chipsBio-chips Added Functional Diversity: More interaction Sensory parts: Measuring and sense surrounding Brain: Computation and Calculations HigherValueSystems Faster processing and better interaction with environment holds the key to next-gen technologies. MM and MtM are the solutions !!! Faster processing and better interaction with environment holds the key to next-gen technologies. MM and MtM are the solutions !!! How to get more ??? 5
Abhijeet Paul ITRS CMOS scaling challenges Intel Need higher processing Speed !!! Need for faster Transistors!!! CMOS challengesCMOS challenges New MaterialsNew Materials SiNW FET New device structure New device structure Next-gen CMOS scaling solutions More MooreNext-gen CMOS scaling solutions More Moore 6 Revolutionary Evolutionary
Abhijeet Paul www.tellurex.com Choudhary et. al, Nature nano. (2009) Why thermoelectricity ??? Increasing pollution!!! IEA, WEO, 2008 Increasing energy dem and!!! Gelsinger et. al ISSCC 2001 Increasing IC heat!!! Nasty ProblemsNasty Problems On chip thermoelectric cooling (BiTe SL) DEER Automobile waste heat thermoelectric power generation Green energy Production by thermoelectricity Green Solutions from thermoelectricity More than MooreGreen Solutions from thermoelectricity More than Moore 7
Abhijeet Paul Dimensional Scaling: CMOS 2003 2005 2007 2009 2011 StrainTechnology High-k MetalGate 3D FETS SiGe strained High-K MG From bulk planar to 3D nano-scale SiNW FET III-V FET Graphene CNT-FET Non-Si 3D FETs are a solution Non-Si 3D FETs are a solution ? ? ? 8 IBM
Abhijeet Paul Dimensional scaling: Thermoelectricity BiTe/PbTe Qwell Superlattice SiGe/Si QDot Superlattice BiTe,PbTe Bulk LAST 1950 2000 1990 1980 1970 1960 2010 Therm oelectric Material developm ent Year line BeginSemiconductoruse (Bi,Sb),(Te,Se),PbTe, PhononGlassElectroncrystal Dresselhauset.al, DOSengg. PbTe Ddots Si /SiGe NW SL Si Nanowires ZT ~1 1< ZT < 3 ZT > 3 From Bulk to Nanostructures … . 9 Atomic scale interface treatment ?? Phonons in nanostructures ?? Treatment of alloys at atomic level ?? Electronic structure in nanostructures? ??? ?? ? Understanding of nano-scale electronic and thermal properties must !! Understanding of nano-scale electronic and thermal properties must !!
Abhijeet Paul Need for Atomic level modeling… Si n-FinFET IMEC H=65nm,W=25nm G. Tettamanzi et. al, EDL, 2009. Intel SiGe pMOSFET IEDM 2010 Ultra-scale geometry with finite atoms Ultra-scale geometry with finite atoms An increasing need for atomic scale modeling to simulate ultra- scaled devices!!! An increasing need for atomic scale modeling to simulate ultra- scaled devices!!! 10 http://www.xray.cz/xray/csca/ kol2010/abst/cechal.htm Quantum Dot Material variation at atomic scale Material variation at atomic scale Atomic scale strain variation Atomic scale strain variation
Abhijeet Paul Need for integrated device modeling … SiGe Si SiO2 Treatment of multiple valleys Treatment of multiple valleys Treatment of multiple materials Treatment of multiple materials Electron current Phonons Treatment of multiple particles Treatment of multiple particles An increasing need for integrated modeling to handle complex issues in device modeling !!! An increasing need for integrated modeling to handle complex issues in device modeling !!! 11
Abhijeet Paul ITRS on the future device modeling ... ITRS 2010, chapter 9, http://www.itrs.net Physical models for stress induced device performance. Physical models for novel materials eg. High-k stacks, Ge and compound III/V channels: … Morphology, Bandstructure, defects/traps,etc. General , accurate, computationally efficient and robust quantum based simulators incl. fundamental parameters linked to electronic bandstructure and phonon spectra. Treatment of individual dopant atoms and traps… Need for an integrated approach to model material, electronic and lattice properties at the atomic scale. Need for an integrated approach to model material, electronic and lattice properties at the atomic scale. 12
Abhijeet Paul Outline of the talk • Motivation »Why the present work is important ? »Need for integrated atomistic simulation framework • Computational modeling and simulation approaches. • Application of the methods to Si nanowires (SiNWs). • Application to non-Si system  GaAs a quick look !! • Global dissemination of findings  nanoHUB.org • Summary • Future directions 13
Abhijeet Paul How to study the nano-scale devices? Bottom-up Approach To nano-scale devices Bottom-up Approach To nano-scale devices ElectronicStructure LatticeStructure Carrier Transport Atomistic Tight-binding (TB) model Atomistic Tight-binding (TB) model 14
Abhijeet Paul <111> Atomistic Tight binding Approach 15 Crystal structureCrystal structure FEATURES/ADVANTAGES Nearest neighbor atomic bond model with spin orbit (SO) coupling.  Based on localized atomic orbital treatment.  Appropriate for treating atomic level disorder.  Strain treatment at atomic level.  Structural and material variation treated easily.  Potential variations can be accounted for (easily). FEATURES/ADVANTAGES Nearest neighbor atomic bond model with spin orbit (SO) coupling.  Based on localized atomic orbital treatment.  Appropriate for treating atomic level disorder.  Strain treatment at atomic level.  Structural and material variation treated easily.  Potential variations can be accounted for (easily). Y Z <100> (x)<110> StructureStructure OrbitalOrbital InteractionInteraction AssembleAssemble TB HamiltonianTB Hamiltonian Atomistic Tight Binding (TB) A reliable way to calculate electronic structure in ultra-scaled structures. Atomistic Tight Binding (TB) A reliable way to calculate electronic structure in ultra-scaled structures. 15
Abhijeet Paul Bulk Bandstructure using Tight-binding Si Lent et. al, Superlat. and Microstruc., 1986 Pb Se sp3 d5 s*-SO model sp3 d5 -SO model Γ  VB  L X  CB  L Atomistic Tight-Binding method  A robust and accurate electronic structure model Atomistic Tight-Binding method  A robust and accurate electronic structure model Zincblende Rocksalt LL 16
Abhijeet Paul Application of TB to FETs: Charge-potential self-consistent approach Schrodinger-Poisson self-consistent solution  Electron transport analysis in nano-scale FETs. Schrodinger-Poisson self-consistent solution  Electron transport analysis in nano-scale FETs. 17
Abhijeet Paul Experimental validation of 2D atomistic Schrodinger-Poisson simulator Collaboration between Purdue University & Institute of Microelectronics, Singapore (2007-08). TEM image of Experimental SiNW FET Device Dimensions: Tox = 9nm W = 25nm H = 14 nm Source/Drain doping : n- type ,1e20cm-3 Intrinsic <100> oriented Silicon channel. Schrodinger using TB 2D FEM Poisson solution 4505 atoms4505 atoms ~20K FEM elements~20K FEM elements chargecharge potentialpotential Self-consistent Simulation Self-consistent simulation of realistic devices using parallel C/C++ code. Self-consistent simulation of realistic devices using parallel C/C++ code. 18
Abhijeet Paul Experimental validation of atomistic simulator contd. Electrical Potential Distribution. Electron charge distribution Self-consistent Simulation Terminal CV benchmarking Good matchingGood matching Impact: Work published in IEEE, EDL VOL. 30, NO. 5,MAY 2009. p.526 Impact: Work published in IEEE, EDL VOL. 30, NO. 5,MAY 2009. p.526 Simulator benchmarked !!! Quantum mechanical simulations for realistic FETs possible. Simulator benchmarked !!! Quantum mechanical simulations for realistic FETs possible. 19
Abhijeet Paul How to study the nano-scale devices? Bottom-up Approach To nano-scale devices Bottom-up Approach To nano-scale devices ElectronicStructure LatticeStructure Carrier Transport Atomistic Tight-binding (TB) model Atomistic Tight-binding (TB) model Modified Valence Force Field (MVFF) model Modified Valence Force Field (MVFF) model 20
Abhijeet Paul Phonon dispersion calculation: Modified VFF (MVFF) model Old Keating Model [1] [A] Bond-stretching(α) Δr [B] Bond-bending(β) Δθ [C] Cross-bond stretch bend (γ) [2] Zunger et. al. 1999Δθ Δr Imp. For polar materials [2] Imp. for polar materials [2] [F] Coulomb interaction [E] Δθ1 Δθ2 Coplanar bond bending(τ) Imp. for non-polar materials ([3] Sui et. al, [D] Δr1 Δr2 Cross bond Stretching (δ) Short Range Short Range [1] Keating. Phys. Rev. 145, 1966. [2] PRB, 59,2881, 1999. [3] PRB, 48, 17938,1993 Long Range Long Range 21 New combination of Interactions: Modified Valence Force Field Calculate phonons in zinc-blende materials. New combination of Interactions: Modified Valence Force Field Calculate phonons in zinc-blende materials.
Abhijeet Paul Bulk Si Expt. (dots) [1] What is the need for a new phonon model?? Accurate phonon model crucial for correct calculation of phonon dispersion in nanostructures. Accurate phonon model crucial for correct calculation of phonon dispersion in nanostructures. Bulk Si Expt. (dots) [1] [1] Nelsin et. al, PRB, 6, 3777, 1972. 22 Keating VFF Model Over estimates acoustic modes at zone edges. Over estimates optical modes New MVFF model matchs the dispersion very well in the entire Brillouin zone !!! Expt. Data[1], inelastic neutron scattering (80K and 300K). Expt. Data[1], inelastic neutron scattering (80K and 300K).
Abhijeet Paul 1D periodic [100] Si nanowire structure. Surface atoms free to vibrate. 1D periodic [100] Si nanowire structure. Surface atoms free to vibrate. [100] free standing SiNW qx [norm.] X Bulk Si 6 branches Phonon dispersion in free-standing nanowires 23 Strong phonon confinement responsible for different lattice properties in SiNWs compared to bulk. Strong phonon confinement responsible for different lattice properties in SiNWs compared to bulk. Lot of flat bands (zero velocity) resulting in phonon confinement. 2 branches 1 branch 1 branch 2 branches
Abhijeet Paul Approaches to study the nano-scale devices Bottom-up Approach To nano-scale devices Bottom-up Approach To nano-scale devices ElectronicStructure LatticeStructure Carrier Transport Atomistic Tight-binding (TB) model Atomistic Tight-binding (TB) model Modified Valence Force Field (MVFF) model Modified Valence Force Field (MVFF) model Landauer’s model (LM)Landauer’s model (LM) 24
Abhijeet Paul Material A Material B How to analyze thermoelectric properties of materials ? V1 V2 IN O U T Tc Th IQ Ie Ie Steady-state linear thermoelectric (Onsager’s) relations [1,2] [1] L. Onsager, Phys. Rev. 37 405 (1931). [2] G. D. Mahan, Many-body Physics. lehhch TTTTTTVVV   ,2,,21 TT q Tk V B  Landauer’s Formula can be used to evaluate the transport parameters Landauer’s Formula can be used to evaluate the transport parameters     TTGSVTGSIQ  .. 2   TGSVGIe  .. Electric current Heat current 25
Abhijeet Paul Goodness of thermoelectric materials: Figure of Merit (ZT) T V   S Generation of potential difference due to applied temperature difference`Seebeck Coefficient’. Generation of potential difference due to applied temperature difference`Seebeck Coefficient’. Generation of temperature difference due to applied potential difference  `Peltier Coefficient’ Generation of temperature difference due to applied potential difference  `Peltier Coefficient’ Measure of thermoelectric power generation (High) T V T    Measure of thermoelectric cooling (High) Ability of material to conduct electricity `Electrical Conductance’ Ability of material to conduct electricity `Electrical Conductance’ V I G    Measure of charge flow (High) d Q T    1  Ability of material to conduct heat energy `Thermal Conductance’ Ability of material to conduct heat energy `Thermal Conductance’ Measure of heat flow (Low) Both electrons (ke)and lattice(kl) carry heat. ZT = ‘Thermoelectric Figure of Merit’  by Ioffe in 1949. S2 G = Electronic Power Factor (PF) ZT = ‘Thermoelectric Figure of Merit’  by Ioffe in 1949. S2 G = Electronic Power Factor (PF)el TGS ZT    2 26 High ZT  large G large S and small κ desired !!!High ZT  large G large S and small κ desired !!!
Abhijeet Paul Calculation of thermoelectric parameters 27 )(factor-Pre /le mLf G,S κe (Electronic) Landauer’s approach  A suitable approach to calculate thermoelectric transport parameters in nanostructures. Landauer’s approach  A suitable approach to calculate thermoelectric transport parameters in nanostructures. κl (Lattice) Landauer’s IntegralLandauer’s Integral Under zero current condition e LG 0 ee LLS 01 / l l L1
Abhijeet Paul A closer look at electrons and phonons 28                  max 0 )( )()(    dM T F L L BEphml m Phonon IntegralPhonon Integral                         Etop FDel m B e m dEEM E EF L E Tk EfE L )( )()( Electron IntegralElectron Integral le mL / •No. of modes, M(E). •Mean free path (λ). Both need •Moment calculation near Fermi Level •Fermi Dirac distribution (fermions!!) •M(E)  Electronic bandstructure. Electrons need •No Fermi Level •Bose Einstein distribution (bosons!!) • M(ω)  Phonon dispersion. Phonons need Accurate electronic & phonon dispersions must !!!. Accurate electronic & phonon dispersions must !!!.
Abhijeet Paul The complete approach set Bottom-up Approach To nano-scale devices Bottom-up Approach To nano-scale devices ElectronicStructure LatticeStructure Carrier Transport Atomistic Tight-binding (TB) model Atomistic Tight-binding (TB) model Modified Valence Force Field (MVFF) model Modified Valence Force Field (MVFF) model Landauer’s model (LM)Landauer’s model (LM) Electronic Properties Electronic Properties Thermal Properties Thermal Properties ThermoelectricityThermoelectricity An ‘integrated approach’ to study electronic, physical and thermal properties of nanostructures !!! An ‘integrated approach’ to study electronic, physical and thermal properties of nanostructures !!! 29
Abhijeet Paul Outline of the talk • Motivation »Why the present work is important ? »Need for integrated atomistic simulation framework • Computational modeling and simulation approaches. • Application of the methods to Si nanowires (SiNWs). • Application to non-Si system  GaAs a quick look !! • Global dissemination of findings  nanoHUB.org • Summary • Future direction 30
Abhijeet Paul SiNW Explosive -sensor [E] Silicon nanowires (SiNW): The vast potential [A] Yang et. al, 2010, Nanoletters. [B] Kalzenberg et. al, 2008, Nanoletters. [C] Chin et. al, 2009, IEEE, TED. [D] Hochbaum et. al, 2008, Nature. [E] Patlosky et. al, 2010, Verlag, Germany. Cathode Li2S Anode SiNW Batteries [A] Silicon nanowire Solar cells [B] Transistors [C] Thermoelectricity [D]SiNWs have versatile applications and are highly compatible to CMOS. Interesting system to study!!! SiNWs have versatile applications and are highly compatible to CMOS. Interesting system to study!!! 31
Abhijeet Paul Nanoscale solutions in SiNWs Silicon nanowire Physical metrology How to determine size, shape and orientation ? Electrical metrology How to determine interface traps in SiNW FETs? Thermal properties How to engineer thermal properties of SiNW ? Thermoelectricity How to enhance PF and ZT of SiNW ? ?? 32
Abhijeet Paul Peeking into the channel of Si trigated n-FinFETs 33 Collaboration between Purdue University ,TU Delft, Netherlands and IMEC, Belgium (2009-2011). TEM image of tri-gated n-FinFETs Active Area(SAA) Where do the charges flow ? source Channel Barrier Height (Eb) How easily charges go from source to channel? Temperature Based G-V measurement Experiment From slope From intercept Sub-threshold thermionic current provides information about undoped channel Si FinFETs !!! Sub-threshold thermionic current provides information about undoped channel Si FinFETs !!!
Abhijeet Paul Trends of Eb and SAA in Si n-FinFET: Experiment vs. Simulation 34 Experimental ResultsEb and SAA decrease with Vgs  volume to surface inversion Simulated Tri-gated Si n-FinFET Schrodinger Eq.: 20 band sp3 d5 s* model with spin orbit coupling for Si. Schrodinger Eq.: 20 band sp3 d5 s* model with spin orbit coupling for Si. 2D-Poisson Solution2D-Poisson Solution ρ(r) V(r) Simulation Approach Simulation Approach Performed using OMEN-3Dpar Channel with ~44K atoms (support from Sunhee Lee) Good match !! ??? Simulations give good qualitative match !! What is the reason for mismatch in SAA ? Simulations give good qualitative match !! What is the reason for mismatch in SAA ?
Abhijeet Paul Mismatch in SAA : Interface trap density (Dit) extraction 35 A B 3D FinFETs bad sidewall etch [1] interface traps gate screened from channel mismatch in SAA [1] Kapila et. al, IEEE, EDL, 2008 From Charge Neutrality ~2X~2X No H2 anneal More mismatch!! No H2 anneal More mismatch!! A. Paul et. al, JAP, 2011 Difference in expt. and simulated SAA  Dit extraction  Method 1 H2 anneal reduce traps by ~2X. Difference in expt. and simulated SAA  Dit extraction  Method 1 H2 anneal reduce traps by ~2X.
Abhijeet Paul Mismatch in Eb : Interface trap density (Dit) extraction 36Gate Voltage (V) Eb(meV) H2 anneal H2 anneal 3D FinFETs bad sidewall etch [1] interface traps gate screened from channel mismatch in Eb g b V E    Gate to Channel coupling. Suppressed by interface traps Dit ~18.1x1011 #/cm2 Dit ~15.3x1011 #/cm2 [110] Dit ~10.3x1011 #/cm2 [100]Difference in expt. and simulated α  Dit extraction  Method 2 [110] sidewall Dit > [100] sidewall Dit. Difference in expt. and simulated α  Dit extraction  Method 2 [110] sidewall Dit > [100] sidewall Dit. A.Paul et. al, JAP, 2011
Abhijeet Paul Conductance Measurement and simulations. Conductance Measurement and simulations. Silicon nanowire Physical metrology How to determine size, shape and orientation ? Electrical metrology How to determine interface traps in SiNW FETs? Thermal properties How to engineer thermal properties of SiNW ? Thermoelectricity How to enhance PF and ZT of SiNW ? ?? 37
Abhijeet Paul Physical Metrology  Raman Spectroscopy: A primer Frequency(cm-1 ) Intensity (a.u) Bulk Material Nanostructure (NS) Phonon Shift  Raman Spectrometer Phonon Shift  Raman Spectrometer Acoustic Phonon shift Acoustic Phonon shift q  Frequency(ω) Optical Phonon shift Optical Phonon shift q  Frequency(ω) Bulk / NS // acoptacoptacopt   2 types of shifts ∆ω > 0  Blue-shift ∆ω < 0  Red-shift Info on size, dimensionality, crystallanity of nanostructuresPhonon shifts provide vital information about Physical properties of nanostructures!!! Phonon shifts provide vital information about Physical properties of nanostructures!!! 38
Abhijeet Paul Phonon shifts: Experimental benchmarking. Acoustic hardening or blue-shift in SiNWs Acoustic hardening or blue-shift in SiNWs Optical softening or red-shift in SiNWs Optical softening or red-shift in SiNWs 39 d        W a A 0  Connects to dimensionality of NS Connects to the shape of the nanowire in 1D MVFF compares with expts. very well Acoustic d <1 for 1D. A >0 Optical d >1 for 1D. A < 0 MVFF provides correct trend for phonon shifts  ‘A’ and ‘d’ correlation can connect to SiNW shape MVFF provides correct trend for phonon shifts  ‘A’ and ‘d’ correlation can connect to SiNW shape
Abhijeet Paul Physical metrology of SiNWs 40 SiNW shapes under study d        W a A 0  ‘A’ and ‘d’ from acoustic and optical phonon shifts correlate to SiNW shape nanoscale metrology ‘A’ and ‘d’ from acoustic and optical phonon shifts correlate to SiNW shape nanoscale metrology
Abhijeet Paul Conductance Measurement and simulations. Conductance Measurement and simulations. Silicon nanowire Physical metrology How to determine size, shape and orientation ? Electrical metrology How to determine interface traps in SiNW FETs? Thermal properties How to engineer thermal properties of SiNW ? Thermoelectricity How to enhance PF and ZT of SiNW ? Raman spectroscopy Phonon shift in SiNWs Raman spectroscopy Phonon shift in SiNWs ?? 41
Abhijeet Paul Heat SinkHeat Sink BB AA Heat SourceHeat Source Thermoelectric device Need for tuning material thermal properties 42 HeatFlow Thermal Capacitance VCV  thC Equivalent thermal circuit Thermal Resistance L A th    thR Engineering material thermal properties can improve system performance!!! Engineering material thermal properties can improve system performance!!! Better Laser Cooling Better Heat evacuation in FETs. Improved ZT in thermoelectric devices
Abhijeet Paul Strain: Tuning thermal conductivity of SiNWs Set-up Expt. Result Gan et.al Purdue University MVFF simulations show similar tuning for thermal conductivity with strain. MVFF simulations show similar tuning for thermal conductivity with strain. Simulation MVFF A. Paul et. al, APL, 2011. 43
Abhijeet Paul Engineering κl using strain in SiNW Phonon energy range 0 -22 meV Low 22-44 meV Mid 44-65 meV High Strain type Compressive  Tensile (-2%+2%) Uniaxial 36%34% 52%50% 12%13% Hydrostatic 32%37% 56%45% 11%16% 44 Energy Spectral Contribution κl κl increases under compressive uniaxial strain κl is weakly sensitive to hydrostatic strain Low and mid range bands responsible. Low and high bands oppose mid bands  overall negligible change Uniaxial strain tunes κl more than hydrostatic strain in SiNWs!! Uniaxial strain tunes κl more than hydrostatic strain in SiNWs!!
Abhijeet Paul Tuning Specific heat (Cv) of SiNWs using strain 45 Uniaxial strain brings neglible change to Cv Very less change In energy contribution under strain Hydrostatic strain brings large change to Cv Higher energy bands contribute to the change in Cv. Hydrostatic strain tunes Cv more than uniaxial strain in SiNWs !!! Hydrostatic strain tunes Cv more than uniaxial strain in SiNWs !!!
Abhijeet Paul Conductance Measurement and simulations. Conductance Measurement and simulations. Silicon nanowire Physical metrology How to determine size, shape and orientation ? Electrical metrology How to determine interface traps in SiNW FETs? Thermal properties How to engineer thermal properties of SiNW ? Thermoelectricity How to enhance PF and ZT of SiNW ? Strain tunes Phonon thermal properties Strain tunes Phonon thermal properties ?? Raman spectroscopy Phonon shift in SiNWs Raman spectroscopy Phonon shift in SiNWs 46
Abhijeet Paul Porous crystalline Si for thermoelectricity Hopkins et.al Nano. Lett., 2011. Tang et.al Nano Lett., 2010. Yu et. al Nature Nanotech. 2010 Electrical Conductivity[1] Electrical Conductivity[1] ~1.5X Drop Thermal Conductivity[1] Thermal Conductivity[1] ~8X Reduction  Experimental structures Experimental structures Experimental results Experimental results [1] Yu et. al Nature Nanotech., 2010. Porous Silicon  an attractive alternative for RT thermoelectric material. How about porous SiNWs ? Porous Silicon  an attractive alternative for RT thermoelectric material. How about porous SiNWs ? 47
Abhijeet Paul Electronic and Phonon dispersion: Porous SiNW Rh=0.4 nm Dsep=0.2 to 1 nm Hollow SiNW: [100], W=4nm Tight Binding Tight Binding Increase in Ec  more confinement More flat bands  Suppression of heat flow.MVFFMVFF Increased electron and phonon confinement in porous SiNWs compared to filled nanowire. Increased electron and phonon confinement in porous SiNWs compared to filled nanowire. 48
Abhijeet Paul Electrical and thermal transport parameters  Landauer’s method with scattering Electrical and thermal transport parameters  Landauer’s method with scattering Electron and Phonon dispersionElectron and Phonon dispersion Porous SiNWs: Electronic and lattice contribution to ZT ~7% drop  ~35% drop  T )( GS ZT l 2    e Thermoelectric Efficiency Thermoelectric Efficiency PF (S2 G) reduction ~49%  ~55% drop  kl reduction ~55%  Interplay of PF and κl determine the final ZT !!!Interplay of PF and κl determine the final ZT !!! 49 Solid nanowire
Abhijeet Paul Porous SiNW: Power-factor and ZT ~49% drop  ~7% rise  Large reduction in Electrical power-factor due to pores. ZT improves due to large suppression on lattice thermal conductivity. ZT in porous SiNW improves but at the expense of electrical performance !!! ZT in porous SiNW improves but at the expense of electrical performance !!! 50
Abhijeet Paul Conductance Measurement and simulations. Conductance Measurement and simulations. Silicon nanowire Physical metrology How to determine size, shape and orientation ? Electrical metrology How to determine interface traps in SiNW FETs? Thermal properties How to determine thermal properties of SiNW ? Phonons  Lattice thermal properties Phonons  Lattice thermal properties Thermoelectricity How to enhance PF and ZT of SiNW ? Porous SiNW Enhance ZT Porous SiNW Enhance ZT Raman spectroscopy Phonon shift in SiNWs Raman spectroscopy Phonon shift in SiNWs Integrated modeling approach sheds light on many nano-scale aspects of SiNWs. Integrated modeling approach sheds light on many nano-scale aspects of SiNWs. 51
Abhijeet Paul Key new findings and accomplishments • Developed two new interface trap metrology methods in Si trigated FinFETs. »Methods are complimentary and repeatable. (Published in JAP, 2011, IEEE EDL 2010, IEEE EDL 2009) • Correlated the shape and size of SiNWs to phonon shifts  guides Raman Spectroscopy. (Accepted in JAP 2011) • Strain engineering of lattice thermal conductivity and specific heat of SiNWs possible. (Published in APL, 2011) • Possibility of using porous SiNWs for enhanced ZT (~6% rise) at room temperature shown. 52
Abhijeet Paul Outline of the talk • Motivation »Why the present work is important ? »Need for integrated atomistic simulation framework • Computational modeling and simulation approaches. • Application of the methods to Si nanowires (SiNWs). • Application to non-Si system  GaAs a quick look !! • Global dissemination of findings  nanoHUB.org • Summary • Future directions 53
Abhijeet Paul GaAs nanostructures: Electronic and thermoelectric enhancement 54 SiNWSiNW GaAs [100]/(100) ~38% inc. in ION for 4% strain p-type. Integrated Modeling Approach Integrated Modeling ApproachGa GaAs NW 0% 2% 5% kl = 1W/m-K [1] ~10% inc. in ZT for tensile strain n-type [1] Martin et al, Nanoletters, 10, 2010 A. Paul et. al, IEEE Nano, 2011 A. Paul et. al, IEEE DRC, 2011 Integrated modeling performance enhancement of GaAs nanostructures. Integrated modeling performance enhancement of GaAs nanostructures.
Abhijeet Paul Outline of the talk • Motivation »Why the present work is important ? »Need for integrated atomistic simulation framework • Computational modeling and simulation approaches. • Application of the methods to Si nanowires (SiNWs). • Application to non-Si system  GaAs a quick look !! • Global dissemination of findings  nanoHUB.org • Summary • Future directions 55
Abhijeet Paul Global scientific outreach using nanoHUB.org •C/C++ and Matlab based tools. •Enables research in electronic structure and thermoelectricity 56 Open research tool for fellow researchers !!! Open research tool for fellow researchers !!! BandStructure Lab LANTEST Tool Research Tools Most popular tool on nanoHUB. Over 3K users. Till now ran 34503 simulations. Has been cited 28 times in research.
Abhijeet Paul Global semiconductor education using nanoHUB.org 57 Semiconductor Educational Tools Crystal Viewer Tool Periodic Potential lab • 6 C/C++ and MATLAB based semiconductor physics tools developed. •Used in EE305 (Semiconductor Introduction) at Purdue University  Users (last 12 months) = 887  Simulations (last 12 months) ~3K Enabled dissemination of device physics knowledge globally. Enabled dissemination of device physics knowledge globally.
Abhijeet Paul Outline of the talk • Motivation »Why the present work is important ? »Need for integrated atomistic simulation framework • Computational modeling and simulation approaches. • Application of the methods to Si nanowires (SiNWs). • Application to non-Si system  GaAs a quick look !! • Global dissemination of findings  nanoHUB.org • Summary • Future directions 58
Abhijeet Paul Summary • An integrated modeling approach developed to study nanoscale devices. • SiNWs : »Electrical metrology  trap extraction method. »Structural metrology  Raman spectroscopy  phonon shift »Thermal property tuning  Phonon confinement. »Thermoelectricity  Porosity control. 59
Abhijeet Paul Summary • GaAs: »Compressive strain and body scaling enhances ION of UTB p- FETs. »Tensile strain and orientation enhances ZT of GaAs nanowires. • Global outreach for research using nanoHUB.org. 60
Abhijeet Paul Outline of the talk • Motivation »Why the present work is important ? »Need for integrated atomistic simulation framework • Computational modeling and simulation approaches. • Application of the methods to Si nanowires (SiNWs). • Application to non-Si system  GaAs a quick look !! • Global dissemination of findings  nanoHUB.org • Summary • Future directions 61
Abhijeet Paul Future directions • Combining electrons and phonons for better eletro-thermal understanding in nano-scale devices. • Increased device to system level interaction for better design optimizations. 62 http://www.comsol.com/papers/6801/
Abhijeet Paul Future directions • Inclusion of thermodynamics into phonon calculations. • Investigation of source to drain tunneling for performance evaluation of ultra-short MOSFETs. 63 Lattice thermal expansion Si bulk http://www.ioffe.ru/SVA/NSM/Semicond/Si
Abhijeet Paul Thank you!!! 64
Abhijeet Paul Appendix A • References for Acoustic phonon shift »Si-1/Si-2: T. Thonhauser et. al, PRB, 69, 2004. (T) »Si-3: Hepplestone et. al., APL, 87, 2005. (T) • References for Optical phonon shift: »Si-1: Hepplestone et. al., APL, 87, 2005. (T) »Si-2: K. Adu et. al, App. Phys. A, 85, 2006. (E) »Si-3: Sun et. al, PRB, 72, 2005. (T) »Si-4: Campbell et. Al, Solid State Comm., 58, 1986. (T) »Si-5: Zi et. Al, APL, 69, 1996. (T) »Si-6: Yang et. Al, Jour. Phys. Chem., 112, 2008. (E) »Si-7: Faraci et. Al, Journ. App. Phys., 109, 2011. (T) T = Theory , E = Expt. 65

More Related Content

DOC
Opal and inverse opal structures for optical device applications
byM. Faisal Halim
 
PDF
Le Van Hai- Resume
byLe Hai
 
PPT
Nanotechnology Presentation For Electronic Industry
bytabirsir
 
PDF
Nanotechnology and computer science
byJamyang Lotus
 
PPTX
Nanoelectronics
byQazi Raza Abdul Quadir
 
PPT
Nano-electronics
byAbhishek Syal
 
PDF
AC PERFORMANCE OF NANO ELECTRONICS SEMINAR REPORT
bygautam221094
 
PPT
.Nano road
byHebatalrahman Ahmed
 
Opal and inverse opal structures for optical device applications
byM. Faisal Halim
 
Le Van Hai- Resume
byLe Hai
 
Nanotechnology Presentation For Electronic Industry
bytabirsir
 
Nanotechnology and computer science
byJamyang Lotus
 
Nanoelectronics
byQazi Raza Abdul Quadir
 
Nano-electronics
byAbhishek Syal
 
AC PERFORMANCE OF NANO ELECTRONICS SEMINAR REPORT
bygautam221094
 
.Nano road
byHebatalrahman Ahmed
 

What's hot

PPT
Nanotechnology And Its Applications
bymandykhera
 
PPSX
Nanoelectronics
byBharani Dharan
 
DOCX
Nano vlsi
byHossam Zein
 
PDF
nanotechnology
byDeepu PV Reddy
 
PPT
Nanotechnology
byNajiya Kpp
 
PPT
APPLICATIONS OF NANOTECHNOLOGY IN ELECTRONICS.
byVIKAS KUMAR
 
PPT
Nanoelectronics Final
byshikha2510
 
PPTX
Nanotechnology Application (Physics)
bySaharsh Anand
 
PPTX
Nanoelectronics
byAswin Sreeraj
 
PPT
Nano computing
bymanpreetgrewal
 
PDF
Pomrenke - Optoelectronic Information Processing - Spring Review 2012
byThe Air Force Office of Scientific Research
 
PPT
Presentacion De Logica 2
byjeshuel
 
PPT
Nanomachines
byMechanical Online
 
PPTX
Nanotechnology & its Nanowires Application (By-Saquib Khan)
bySAQUIB KHAN
 
PDF
Vanzee 1201
byasim8704
 
PPTX
Electron Microscopy - Scanning electron microscope, Transmission Electron Mic...
bySumer Pankaj
 
PPTX
Nanotechnology
byViju Jigajinni
 
PDF
CV July 2016
byDavid Goren
 
PDF
Aml series piezoelectric materials green energy and sensing - crossing point
byMariya Aleksandrova
 
PPTX
Nanomaterial and meta materials
byDeepak Raj
 
Nanotechnology And Its Applications
bymandykhera
 
Nanoelectronics
byBharani Dharan
 
Nano vlsi
byHossam Zein
 
nanotechnology
byDeepu PV Reddy
 
Nanotechnology
byNajiya Kpp
 
APPLICATIONS OF NANOTECHNOLOGY IN ELECTRONICS.
byVIKAS KUMAR
 
Nanoelectronics Final
byshikha2510
 
Nanotechnology Application (Physics)
bySaharsh Anand
 
Nanoelectronics
byAswin Sreeraj
 
Nano computing
bymanpreetgrewal
 
Pomrenke - Optoelectronic Information Processing - Spring Review 2012
byThe Air Force Office of Scientific Research
 
Presentacion De Logica 2
byjeshuel
 
Nanomachines
byMechanical Online
 
Nanotechnology & its Nanowires Application (By-Saquib Khan)
bySAQUIB KHAN
 
Vanzee 1201
byasim8704
 
Electron Microscopy - Scanning electron microscope, Transmission Electron Mic...
bySumer Pankaj
 
Nanotechnology
byViju Jigajinni
 
CV July 2016
byDavid Goren
 
Aml series piezoelectric materials green energy and sensing - crossing point
byMariya Aleksandrova
 
Nanomaterial and meta materials
byDeepak Raj
 

Viewers also liked

PPTX
Apple i phone 6
byDeepankar Mondal
 
PPT
Народний одяг жителів Рівненщини 19 – поч. 20 століття.
byБібліотека Грем'яче
 
PDF
Help Getting Public Records by Manuel Torres - Monroe, La., NewsTrain - Oct. ...
byNews Leaders Association's NewsTrain
 
PDF
Worth27
bySean McGrath
 
PPTX
Microsoft Office Excel 2013 Tutorials 14- Understanding and Using cell refer...
byMustansir Dahodwala
 
DOCX
wt-43
byDR A.K. SINGH
 
DOCX
Amir CV
byamir sheikh
 
PPSX
GeospatialPresentationWASUP_RobHall
byRob Hall
 
PDF
1. NCRISETM-2017 brochure - Copy
byDR A.K. SINGH
 
PDF
IEDM-2006_Abhijeet_Paul_new
byAbhijeet Paul
 
PPTX
Depression’s Impact on Relationships and Relationships’ Impact on Depression
byUCSF Dept. of Psychiatry
 
DOC
Вікторина «Любов до пізнання»
byБібліотека Грем'яче
 
PPTX
Organizing Music Events - How to Plan & Make Your Plan Works
byCindy Nara
 
PPTX
Genética general | Gatos
byTania Lomeli
 
Apple i phone 6
byDeepankar Mondal
 
Народний одяг жителів Рівненщини 19 – поч. 20 століття.
byБібліотека Грем'яче
 
Help Getting Public Records by Manuel Torres - Monroe, La., NewsTrain - Oct. ...
byNews Leaders Association's NewsTrain
 
Worth27
bySean McGrath
 
Microsoft Office Excel 2013 Tutorials 14- Understanding and Using cell refer...
byMustansir Dahodwala
 
wt-43
byDR A.K. SINGH
 
Amir CV
byamir sheikh
 
GeospatialPresentationWASUP_RobHall
byRob Hall
 
1. NCRISETM-2017 brochure - Copy
byDR A.K. SINGH
 
IEDM-2006_Abhijeet_Paul_new
byAbhijeet Paul
 
Depression’s Impact on Relationships and Relationships’ Impact on Depression
byUCSF Dept. of Psychiatry
 
Вікторина «Любов до пізнання»
byБібліотека Грем'яче
 
Organizing Music Events - How to Plan & Make Your Plan Works
byCindy Nara
 
Genética general | Gatos
byTania Lomeli
 

Similar to PhD_10_2011_Abhijeet_Paul

PPT
Webinar about ATK
byAnders Blom
 
PDF
Ldb Convergenze Parallele_sorba_01
bylaboratoridalbasso
 
PDF
Nano mos25
byMamoon Ismail Khalid
 
PPTX
PhD work on Graphene Transistor
bySouthern University and A&M College - Baton Rouge
 
PDF
Semiconductor nanodevices
byAtif Syed
 
PPTX
Towards atomistic simulation of the electro-thermal properties of,ppts.pptx
byMr M Alam
 
PDF
Research Inventy : International Journal of Engineering and Science is publis...
byresearchinventy
 
PDF
Computational Nano Technology and Simulation Techniques Applied to Study Silv...
byIRJET Journal
 
PPTX
Final Presentation
byRobert Schurz
 
PDF
introduction to nanomaterials- nanotechnology
byAbdEllateefAbbass1
 
PDF
Nanoscale Based Digital VLSI Circuits (1) - NEHA PATEL.pptx.pdf
bybatpad
 
PDF
Nanometric Modelization of Gas Structure, Multidimensional using COMSOL Soft...
byIJECEIAES
 
PPT
Introduction to nano materials
byGulfam Hussain
 
PDF
Physics nanophotonics
byVishal Singh
 
PPT
lugli_slides.ppt
byNirmalM15
 
PDF
Materials Modelling: From theory to solar cells (Lecture 1)
bycdtpv
 
PDF
Theory Of Modern Electronic Semiconductor Devices Kevin F Brennan
bygopiekweonhl
 
PPTX
mosfet and research presentationvxc.pptx
bysrijeett
 
PPTX
Introduction about semiconductors and their integration with nanomaterial
byAbhay Rajput
 
PDF
RASCmar2010
byguest246960
 
Webinar about ATK
byAnders Blom
 
Ldb Convergenze Parallele_sorba_01
bylaboratoridalbasso
 
Nano mos25
byMamoon Ismail Khalid
 
PhD work on Graphene Transistor
bySouthern University and A&M College - Baton Rouge
 
Semiconductor nanodevices
byAtif Syed
 
Towards atomistic simulation of the electro-thermal properties of,ppts.pptx
byMr M Alam
 
Research Inventy : International Journal of Engineering and Science is publis...
byresearchinventy
 
Computational Nano Technology and Simulation Techniques Applied to Study Silv...
byIRJET Journal
 
Final Presentation
byRobert Schurz
 
introduction to nanomaterials- nanotechnology
byAbdEllateefAbbass1
 
Nanoscale Based Digital VLSI Circuits (1) - NEHA PATEL.pptx.pdf
bybatpad
 
Nanometric Modelization of Gas Structure, Multidimensional using COMSOL Soft...
byIJECEIAES
 
Introduction to nano materials
byGulfam Hussain
 
Physics nanophotonics
byVishal Singh
 
lugli_slides.ppt
byNirmalM15
 
Materials Modelling: From theory to solar cells (Lecture 1)
bycdtpv
 
Theory Of Modern Electronic Semiconductor Devices Kevin F Brennan
bygopiekweonhl
 
mosfet and research presentationvxc.pptx
bysrijeett
 
Introduction about semiconductors and their integration with nanomaterial
byAbhay Rajput
 
RASCmar2010
byguest246960
 

PhD_10_2011_Abhijeet_Paul

  • 1.
    Network for Computational Nanotechnology(NCN)Purdue, Norfolk State, Northwestern, MIT, Molecular Foundry, UC Berkeley, Univ. of Illinois, UTEP Electronic and Thermal properties of  semiconductor nanostructures: A modeling and simulation study Abhijeet Paul Network for Computational Nanotechnology  (NCN), Electrical and Computer Engineering Purdue University email: abhijeet.rama@gmail.com 
  • 2.
    Abhijeet Paul Acknowledgements • Overallguidance and direction » Prof. Gerhard Klimeck, Prof. Mark Lundstrom, Purdue University, USA. » Prof. Timothy Boykin, University of Alabama at Huntsville, USA (PhD committee member). » Prof. Leonid Rokhinson, Purdue University, USA (PhD committee member). • Theory and Code development » Dr. Mathieu Luisier, ETH Zurich, Switzerland (OMEN/OMEN-BSLAB development). » Prof. Timothy Boykin, University of Alabama Huntsville, USA (Tight-Binding and solid state phys. theory) » Dr. Neophytos Neophytou, TU Wien, Austria (Initial MATLAB codes) • Discussions and work » Saumitra Mehrotra, Parijat Sengupta, Shuaib Salamat, Sunhee Lee, Lang Zeng, Mehdi Salmani, Kai Miao, Dr. Raseong Kim and Changwook Jeong, Purdue University. • .Experimental Collaborators » Dr. Giuseppe Tettamanzi, TU Delft, Netherlands, Shweta Deora, IIT Bombay, India, Dr. Subash Rustagi, IME, Singapore, Dr. Mark Rodwell, UCSB, USA. • Summer Undergrad students (for nanohub tools) » Junzhe Geng, Victoria Savikhin, Mohammad Zulkifli, and Siqi Wang, Purdue University. • Funding and Computational Resources » MSD-FCRP, SRC, NSF and MIND for funding. » NCN and nanoHUB.org for computational resources. 2
  • 3.
    Abhijeet Paul PhD timelineand progress [A] N. Singh et. al, EDL 2006 [B] A. Hochbaum et. al, Nature, 2008 [C] Yu et. al, Nature, 2010. [D] Pernot et. al, Nature, 2010. Important experimental works that guided this PhD work.Important experimental works that guided this PhD work. 3
  • 4.
    Abhijeet Paul Outline ofthe talk • Motivation » Why the present work is important ? » Need for integrated atomistic simulation framework • Computational modeling and simulation approaches. • Application of the methods to Si nanowires (SiNWs). • Application to non-Si system  GaAs a quick look !! • Global dissemination of findings  nanoHUB.org • Summary • Future directions 4
  • 5.
    Abhijeet Paul MoreMoore(MM)BeyondSi More thanMoore(MtM)  Beyond CMOS 90 nm 90 nm 65 nm 65 nm 45 nm 45 nm 32 nm 32 nm 22 nm 22 nm BaselineCMOS:CPU,Memory,Logic Analog RF Analog RF SensorSensor Thermo electricity Thermo electricity Bio-chipsBio-chips Added Functional Diversity: More interaction Sensory parts: Measuring and sense surrounding Brain: Computation and Calculations HigherValueSystems Faster processing and better interaction with environment holds the key to next-gen technologies. MM and MtM are the solutions !!! Faster processing and better interaction with environment holds the key to next-gen technologies. MM and MtM are the solutions !!! How to get more ??? 5
  • 6.
    Abhijeet Paul ITRS CMOS scalingchallenges Intel Need higher processing Speed !!! Need for faster Transistors!!! CMOS challengesCMOS challenges New MaterialsNew Materials SiNW FET New device structure New device structure Next-gen CMOS scaling solutions More MooreNext-gen CMOS scaling solutions More Moore 6 Revolutionary Evolutionary
  • 7.
    Abhijeet Paul www.tellurex.com Choudhary et.al, Nature nano. (2009) Why thermoelectricity ??? Increasing pollution!!! IEA, WEO, 2008 Increasing energy dem and!!! Gelsinger et. al ISSCC 2001 Increasing IC heat!!! Nasty ProblemsNasty Problems On chip thermoelectric cooling (BiTe SL) DEER Automobile waste heat thermoelectric power generation Green energy Production by thermoelectricity Green Solutions from thermoelectricity More than MooreGreen Solutions from thermoelectricity More than Moore 7
  • 8.
    Abhijeet Paul Dimensional Scaling:CMOS 2003 2005 2007 2009 2011 StrainTechnology High-k MetalGate 3D FETS SiGe strained High-K MG From bulk planar to 3D nano-scale SiNW FET III-V FET Graphene CNT-FET Non-Si 3D FETs are a solution Non-Si 3D FETs are a solution ? ? ? 8 IBM
  • 9.
    Abhijeet Paul Dimensional scaling:Thermoelectricity BiTe/PbTe Qwell Superlattice SiGe/Si QDot Superlattice BiTe,PbTe Bulk LAST 1950 2000 1990 1980 1970 1960 2010 Therm oelectric Material developm ent Year line BeginSemiconductoruse (Bi,Sb),(Te,Se),PbTe, PhononGlassElectroncrystal Dresselhauset.al, DOSengg. PbTe Ddots Si /SiGe NW SL Si Nanowires ZT ~1 1< ZT < 3 ZT > 3 From Bulk to Nanostructures … . 9 Atomic scale interface treatment ?? Phonons in nanostructures ?? Treatment of alloys at atomic level ?? Electronic structure in nanostructures? ??? ?? ? Understanding of nano-scale electronic and thermal properties must !! Understanding of nano-scale electronic and thermal properties must !!
  • 10.
    Abhijeet Paul Need forAtomic level modeling… Si n-FinFET IMEC H=65nm,W=25nm G. Tettamanzi et. al, EDL, 2009. Intel SiGe pMOSFET IEDM 2010 Ultra-scale geometry with finite atoms Ultra-scale geometry with finite atoms An increasing need for atomic scale modeling to simulate ultra- scaled devices!!! An increasing need for atomic scale modeling to simulate ultra- scaled devices!!! 10 http://www.xray.cz/xray/csca/ kol2010/abst/cechal.htm Quantum Dot Material variation at atomic scale Material variation at atomic scale Atomic scale strain variation Atomic scale strain variation
  • 11.
    Abhijeet Paul Need forintegrated device modeling … SiGe Si SiO2 Treatment of multiple valleys Treatment of multiple valleys Treatment of multiple materials Treatment of multiple materials Electron current Phonons Treatment of multiple particles Treatment of multiple particles An increasing need for integrated modeling to handle complex issues in device modeling !!! An increasing need for integrated modeling to handle complex issues in device modeling !!! 11
  • 12.
    Abhijeet Paul ITRS onthe future device modeling ... ITRS 2010, chapter 9, http://www.itrs.net Physical models for stress induced device performance. Physical models for novel materials eg. High-k stacks, Ge and compound III/V channels: … Morphology, Bandstructure, defects/traps,etc. General , accurate, computationally efficient and robust quantum based simulators incl. fundamental parameters linked to electronic bandstructure and phonon spectra. Treatment of individual dopant atoms and traps… Need for an integrated approach to model material, electronic and lattice properties at the atomic scale. Need for an integrated approach to model material, electronic and lattice properties at the atomic scale. 12
  • 13.
    Abhijeet Paul Outline ofthe talk • Motivation »Why the present work is important ? »Need for integrated atomistic simulation framework • Computational modeling and simulation approaches. • Application of the methods to Si nanowires (SiNWs). • Application to non-Si system  GaAs a quick look !! • Global dissemination of findings  nanoHUB.org • Summary • Future directions 13
  • 14.
    Abhijeet Paul How tostudy the nano-scale devices? Bottom-up Approach To nano-scale devices Bottom-up Approach To nano-scale devices ElectronicStructure LatticeStructure Carrier Transport Atomistic Tight-binding (TB) model Atomistic Tight-binding (TB) model 14
  • 15.
    Abhijeet Paul <111> Atomistic Tightbinding Approach 15 Crystal structureCrystal structure FEATURES/ADVANTAGES Nearest neighbor atomic bond model with spin orbit (SO) coupling.  Based on localized atomic orbital treatment.  Appropriate for treating atomic level disorder.  Strain treatment at atomic level.  Structural and material variation treated easily.  Potential variations can be accounted for (easily). FEATURES/ADVANTAGES Nearest neighbor atomic bond model with spin orbit (SO) coupling.  Based on localized atomic orbital treatment.  Appropriate for treating atomic level disorder.  Strain treatment at atomic level.  Structural and material variation treated easily.  Potential variations can be accounted for (easily). Y Z <100> (x)<110> StructureStructure OrbitalOrbital InteractionInteraction AssembleAssemble TB HamiltonianTB Hamiltonian Atomistic Tight Binding (TB) A reliable way to calculate electronic structure in ultra-scaled structures. Atomistic Tight Binding (TB) A reliable way to calculate electronic structure in ultra-scaled structures. 15
  • 16.
    Abhijeet Paul Bulk Bandstructureusing Tight-binding Si Lent et. al, Superlat. and Microstruc., 1986 Pb Se sp3 d5 s*-SO model sp3 d5 -SO model Γ  VB  L X  CB  L Atomistic Tight-Binding method  A robust and accurate electronic structure model Atomistic Tight-Binding method  A robust and accurate electronic structure model Zincblende Rocksalt LL 16
  • 17.
    Abhijeet Paul Application ofTB to FETs: Charge-potential self-consistent approach Schrodinger-Poisson self-consistent solution  Electron transport analysis in nano-scale FETs. Schrodinger-Poisson self-consistent solution  Electron transport analysis in nano-scale FETs. 17
  • 18.
    Abhijeet Paul Experimental validationof 2D atomistic Schrodinger-Poisson simulator Collaboration between Purdue University & Institute of Microelectronics, Singapore (2007-08). TEM image of Experimental SiNW FET Device Dimensions: Tox = 9nm W = 25nm H = 14 nm Source/Drain doping : n- type ,1e20cm-3 Intrinsic <100> oriented Silicon channel. Schrodinger using TB 2D FEM Poisson solution 4505 atoms4505 atoms ~20K FEM elements~20K FEM elements chargecharge potentialpotential Self-consistent Simulation Self-consistent simulation of realistic devices using parallel C/C++ code. Self-consistent simulation of realistic devices using parallel C/C++ code. 18
  • 19.
    Abhijeet Paul Experimental validationof atomistic simulator contd. Electrical Potential Distribution. Electron charge distribution Self-consistent Simulation Terminal CV benchmarking Good matchingGood matching Impact: Work published in IEEE, EDL VOL. 30, NO. 5,MAY 2009. p.526 Impact: Work published in IEEE, EDL VOL. 30, NO. 5,MAY 2009. p.526 Simulator benchmarked !!! Quantum mechanical simulations for realistic FETs possible. Simulator benchmarked !!! Quantum mechanical simulations for realistic FETs possible. 19
  • 20.
    Abhijeet Paul How tostudy the nano-scale devices? Bottom-up Approach To nano-scale devices Bottom-up Approach To nano-scale devices ElectronicStructure LatticeStructure Carrier Transport Atomistic Tight-binding (TB) model Atomistic Tight-binding (TB) model Modified Valence Force Field (MVFF) model Modified Valence Force Field (MVFF) model 20
  • 21.
    Abhijeet Paul Phonon dispersioncalculation: Modified VFF (MVFF) model Old Keating Model [1] [A] Bond-stretching(α) Δr [B] Bond-bending(β) Δθ [C] Cross-bond stretch bend (γ) [2] Zunger et. al. 1999Δθ Δr Imp. For polar materials [2] Imp. for polar materials [2] [F] Coulomb interaction [E] Δθ1 Δθ2 Coplanar bond bending(τ) Imp. for non-polar materials ([3] Sui et. al, [D] Δr1 Δr2 Cross bond Stretching (δ) Short Range Short Range [1] Keating. Phys. Rev. 145, 1966. [2] PRB, 59,2881, 1999. [3] PRB, 48, 17938,1993 Long Range Long Range 21 New combination of Interactions: Modified Valence Force Field Calculate phonons in zinc-blende materials. New combination of Interactions: Modified Valence Force Field Calculate phonons in zinc-blende materials.
  • 22.
    Abhijeet Paul Bulk Si Expt.(dots) [1] What is the need for a new phonon model?? Accurate phonon model crucial for correct calculation of phonon dispersion in nanostructures. Accurate phonon model crucial for correct calculation of phonon dispersion in nanostructures. Bulk Si Expt. (dots) [1] [1] Nelsin et. al, PRB, 6, 3777, 1972. 22 Keating VFF Model Over estimates acoustic modes at zone edges. Over estimates optical modes New MVFF model matchs the dispersion very well in the entire Brillouin zone !!! Expt. Data[1], inelastic neutron scattering (80K and 300K). Expt. Data[1], inelastic neutron scattering (80K and 300K).
  • 23.
    Abhijeet Paul 1D periodic[100] Si nanowire structure. Surface atoms free to vibrate. 1D periodic [100] Si nanowire structure. Surface atoms free to vibrate. [100] free standing SiNW qx [norm.] X Bulk Si 6 branches Phonon dispersion in free-standing nanowires 23 Strong phonon confinement responsible for different lattice properties in SiNWs compared to bulk. Strong phonon confinement responsible for different lattice properties in SiNWs compared to bulk. Lot of flat bands (zero velocity) resulting in phonon confinement. 2 branches 1 branch 1 branch 2 branches
  • 24.
    Abhijeet Paul Approaches tostudy the nano-scale devices Bottom-up Approach To nano-scale devices Bottom-up Approach To nano-scale devices ElectronicStructure LatticeStructure Carrier Transport Atomistic Tight-binding (TB) model Atomistic Tight-binding (TB) model Modified Valence Force Field (MVFF) model Modified Valence Force Field (MVFF) model Landauer’s model (LM)Landauer’s model (LM) 24
  • 25.
    Abhijeet Paul Material A MaterialB How to analyze thermoelectric properties of materials ? V1 V2 IN O U T Tc Th IQ Ie Ie Steady-state linear thermoelectric (Onsager’s) relations [1,2] [1] L. Onsager, Phys. Rev. 37 405 (1931). [2] G. D. Mahan, Many-body Physics. lehhch TTTTTTVVV   ,2,,21 TT q Tk V B  Landauer’s Formula can be used to evaluate the transport parameters Landauer’s Formula can be used to evaluate the transport parameters     TTGSVTGSIQ  .. 2   TGSVGIe  .. Electric current Heat current 25
  • 26.
    Abhijeet Paul Goodness ofthermoelectric materials: Figure of Merit (ZT) T V   S Generation of potential difference due to applied temperature difference`Seebeck Coefficient’. Generation of potential difference due to applied temperature difference`Seebeck Coefficient’. Generation of temperature difference due to applied potential difference  `Peltier Coefficient’ Generation of temperature difference due to applied potential difference  `Peltier Coefficient’ Measure of thermoelectric power generation (High) T V T    Measure of thermoelectric cooling (High) Ability of material to conduct electricity `Electrical Conductance’ Ability of material to conduct electricity `Electrical Conductance’ V I G    Measure of charge flow (High) d Q T    1  Ability of material to conduct heat energy `Thermal Conductance’ Ability of material to conduct heat energy `Thermal Conductance’ Measure of heat flow (Low) Both electrons (ke)and lattice(kl) carry heat. ZT = ‘Thermoelectric Figure of Merit’  by Ioffe in 1949. S2 G = Electronic Power Factor (PF) ZT = ‘Thermoelectric Figure of Merit’  by Ioffe in 1949. S2 G = Electronic Power Factor (PF)el TGS ZT    2 26 High ZT  large G large S and small κ desired !!!High ZT  large G large S and small κ desired !!!
  • 27.
    Abhijeet Paul Calculation ofthermoelectric parameters 27 )(factor-Pre /le mLf G,S κe (Electronic) Landauer’s approach  A suitable approach to calculate thermoelectric transport parameters in nanostructures. Landauer’s approach  A suitable approach to calculate thermoelectric transport parameters in nanostructures. κl (Lattice) Landauer’s IntegralLandauer’s Integral Under zero current condition e LG 0 ee LLS 01 / l l L1
  • 28.
    Abhijeet Paul A closerlook at electrons and phonons 28                  max 0 )( )()(    dM T F L L BEphml m Phonon IntegralPhonon Integral                         Etop FDel m B e m dEEM E EF L E Tk EfE L )( )()( Electron IntegralElectron Integral le mL / •No. of modes, M(E). •Mean free path (λ). Both need •Moment calculation near Fermi Level •Fermi Dirac distribution (fermions!!) •M(E)  Electronic bandstructure. Electrons need •No Fermi Level •Bose Einstein distribution (bosons!!) • M(ω)  Phonon dispersion. Phonons need Accurate electronic & phonon dispersions must !!!. Accurate electronic & phonon dispersions must !!!.
  • 29.
    Abhijeet Paul The completeapproach set Bottom-up Approach To nano-scale devices Bottom-up Approach To nano-scale devices ElectronicStructure LatticeStructure Carrier Transport Atomistic Tight-binding (TB) model Atomistic Tight-binding (TB) model Modified Valence Force Field (MVFF) model Modified Valence Force Field (MVFF) model Landauer’s model (LM)Landauer’s model (LM) Electronic Properties Electronic Properties Thermal Properties Thermal Properties ThermoelectricityThermoelectricity An ‘integrated approach’ to study electronic, physical and thermal properties of nanostructures !!! An ‘integrated approach’ to study electronic, physical and thermal properties of nanostructures !!! 29
  • 30.
    Abhijeet Paul Outline ofthe talk • Motivation »Why the present work is important ? »Need for integrated atomistic simulation framework • Computational modeling and simulation approaches. • Application of the methods to Si nanowires (SiNWs). • Application to non-Si system  GaAs a quick look !! • Global dissemination of findings  nanoHUB.org • Summary • Future direction 30
  • 31.
    Abhijeet Paul SiNW Explosive -sensor[E] Silicon nanowires (SiNW): The vast potential [A] Yang et. al, 2010, Nanoletters. [B] Kalzenberg et. al, 2008, Nanoletters. [C] Chin et. al, 2009, IEEE, TED. [D] Hochbaum et. al, 2008, Nature. [E] Patlosky et. al, 2010, Verlag, Germany. Cathode Li2S Anode SiNW Batteries [A] Silicon nanowire Solar cells [B] Transistors [C] Thermoelectricity [D]SiNWs have versatile applications and are highly compatible to CMOS. Interesting system to study!!! SiNWs have versatile applications and are highly compatible to CMOS. Interesting system to study!!! 31
  • 32.
    Abhijeet Paul Nanoscale solutionsin SiNWs Silicon nanowire Physical metrology How to determine size, shape and orientation ? Electrical metrology How to determine interface traps in SiNW FETs? Thermal properties How to engineer thermal properties of SiNW ? Thermoelectricity How to enhance PF and ZT of SiNW ? ?? 32
  • 33.
    Abhijeet Paul Peeking intothe channel of Si trigated n-FinFETs 33 Collaboration between Purdue University ,TU Delft, Netherlands and IMEC, Belgium (2009-2011). TEM image of tri-gated n-FinFETs Active Area(SAA) Where do the charges flow ? source Channel Barrier Height (Eb) How easily charges go from source to channel? Temperature Based G-V measurement Experiment From slope From intercept Sub-threshold thermionic current provides information about undoped channel Si FinFETs !!! Sub-threshold thermionic current provides information about undoped channel Si FinFETs !!!
  • 34.
    Abhijeet Paul Trends ofEb and SAA in Si n-FinFET: Experiment vs. Simulation 34 Experimental ResultsEb and SAA decrease with Vgs  volume to surface inversion Simulated Tri-gated Si n-FinFET Schrodinger Eq.: 20 band sp3 d5 s* model with spin orbit coupling for Si. Schrodinger Eq.: 20 band sp3 d5 s* model with spin orbit coupling for Si. 2D-Poisson Solution2D-Poisson Solution ρ(r) V(r) Simulation Approach Simulation Approach Performed using OMEN-3Dpar Channel with ~44K atoms (support from Sunhee Lee) Good match !! ??? Simulations give good qualitative match !! What is the reason for mismatch in SAA ? Simulations give good qualitative match !! What is the reason for mismatch in SAA ?
  • 35.
    Abhijeet Paul Mismatch inSAA : Interface trap density (Dit) extraction 35 A B 3D FinFETs bad sidewall etch [1] interface traps gate screened from channel mismatch in SAA [1] Kapila et. al, IEEE, EDL, 2008 From Charge Neutrality ~2X~2X No H2 anneal More mismatch!! No H2 anneal More mismatch!! A. Paul et. al, JAP, 2011 Difference in expt. and simulated SAA  Dit extraction  Method 1 H2 anneal reduce traps by ~2X. Difference in expt. and simulated SAA  Dit extraction  Method 1 H2 anneal reduce traps by ~2X.
  • 36.
    Abhijeet Paul Mismatch inEb : Interface trap density (Dit) extraction 36Gate Voltage (V) Eb(meV) H2 anneal H2 anneal 3D FinFETs bad sidewall etch [1] interface traps gate screened from channel mismatch in Eb g b V E    Gate to Channel coupling. Suppressed by interface traps Dit ~18.1x1011 #/cm2 Dit ~15.3x1011 #/cm2 [110] Dit ~10.3x1011 #/cm2 [100]Difference in expt. and simulated α  Dit extraction  Method 2 [110] sidewall Dit > [100] sidewall Dit. Difference in expt. and simulated α  Dit extraction  Method 2 [110] sidewall Dit > [100] sidewall Dit. A.Paul et. al, JAP, 2011
  • 37.
    Abhijeet Paul Conductance Measurement and simulations. Conductance Measurement and simulations. Silicon nanowire Physical metrology Howto determine size, shape and orientation ? Electrical metrology How to determine interface traps in SiNW FETs? Thermal properties How to engineer thermal properties of SiNW ? Thermoelectricity How to enhance PF and ZT of SiNW ? ?? 37
  • 38.
    Abhijeet Paul Physical Metrology Raman Spectroscopy: A primer Frequency(cm-1 ) Intensity (a.u) Bulk Material Nanostructure (NS) Phonon Shift  Raman Spectrometer Phonon Shift  Raman Spectrometer Acoustic Phonon shift Acoustic Phonon shift q  Frequency(ω) Optical Phonon shift Optical Phonon shift q  Frequency(ω) Bulk / NS // acoptacoptacopt   2 types of shifts ∆ω > 0  Blue-shift ∆ω < 0  Red-shift Info on size, dimensionality, crystallanity of nanostructuresPhonon shifts provide vital information about Physical properties of nanostructures!!! Phonon shifts provide vital information about Physical properties of nanostructures!!! 38
  • 39.
    Abhijeet Paul Phonon shifts:Experimental benchmarking. Acoustic hardening or blue-shift in SiNWs Acoustic hardening or blue-shift in SiNWs Optical softening or red-shift in SiNWs Optical softening or red-shift in SiNWs 39 d        W a A 0  Connects to dimensionality of NS Connects to the shape of the nanowire in 1D MVFF compares with expts. very well Acoustic d <1 for 1D. A >0 Optical d >1 for 1D. A < 0 MVFF provides correct trend for phonon shifts  ‘A’ and ‘d’ correlation can connect to SiNW shape MVFF provides correct trend for phonon shifts  ‘A’ and ‘d’ correlation can connect to SiNW shape
  • 40.
    Abhijeet Paul Physical metrologyof SiNWs 40 SiNW shapes under study d        W a A 0  ‘A’ and ‘d’ from acoustic and optical phonon shifts correlate to SiNW shape nanoscale metrology ‘A’ and ‘d’ from acoustic and optical phonon shifts correlate to SiNW shape nanoscale metrology
  • 41.
    Abhijeet Paul Conductance Measurement and simulations. Conductance Measurement and simulations. Silicon nanowire Physical metrology Howto determine size, shape and orientation ? Electrical metrology How to determine interface traps in SiNW FETs? Thermal properties How to engineer thermal properties of SiNW ? Thermoelectricity How to enhance PF and ZT of SiNW ? Raman spectroscopy Phonon shift in SiNWs Raman spectroscopy Phonon shift in SiNWs ?? 41
  • 42.
    Abhijeet Paul Heat SinkHeatSink BB AA Heat SourceHeat Source Thermoelectric device Need for tuning material thermal properties 42 HeatFlow Thermal Capacitance VCV  thC Equivalent thermal circuit Thermal Resistance L A th    thR Engineering material thermal properties can improve system performance!!! Engineering material thermal properties can improve system performance!!! Better Laser Cooling Better Heat evacuation in FETs. Improved ZT in thermoelectric devices
  • 43.
    Abhijeet Paul Strain: Tuningthermal conductivity of SiNWs Set-up Expt. Result Gan et.al Purdue University MVFF simulations show similar tuning for thermal conductivity with strain. MVFF simulations show similar tuning for thermal conductivity with strain. Simulation MVFF A. Paul et. al, APL, 2011. 43
  • 44.
    Abhijeet Paul Engineering κlusing strain in SiNW Phonon energy range 0 -22 meV Low 22-44 meV Mid 44-65 meV High Strain type Compressive  Tensile (-2%+2%) Uniaxial 36%34% 52%50% 12%13% Hydrostatic 32%37% 56%45% 11%16% 44 Energy Spectral Contribution κl κl increases under compressive uniaxial strain κl is weakly sensitive to hydrostatic strain Low and mid range bands responsible. Low and high bands oppose mid bands  overall negligible change Uniaxial strain tunes κl more than hydrostatic strain in SiNWs!! Uniaxial strain tunes κl more than hydrostatic strain in SiNWs!!
  • 45.
    Abhijeet Paul Tuning Specificheat (Cv) of SiNWs using strain 45 Uniaxial strain brings neglible change to Cv Very less change In energy contribution under strain Hydrostatic strain brings large change to Cv Higher energy bands contribute to the change in Cv. Hydrostatic strain tunes Cv more than uniaxial strain in SiNWs !!! Hydrostatic strain tunes Cv more than uniaxial strain in SiNWs !!!
  • 46.
    Abhijeet Paul Conductance Measurement and simulations. Conductance Measurement and simulations. Silicon nanowire Physical metrology Howto determine size, shape and orientation ? Electrical metrology How to determine interface traps in SiNW FETs? Thermal properties How to engineer thermal properties of SiNW ? Thermoelectricity How to enhance PF and ZT of SiNW ? Strain tunes Phonon thermal properties Strain tunes Phonon thermal properties ?? Raman spectroscopy Phonon shift in SiNWs Raman spectroscopy Phonon shift in SiNWs 46
  • 47.
    Abhijeet Paul Porous crystallineSi for thermoelectricity Hopkins et.al Nano. Lett., 2011. Tang et.al Nano Lett., 2010. Yu et. al Nature Nanotech. 2010 Electrical Conductivity[1] Electrical Conductivity[1] ~1.5X Drop Thermal Conductivity[1] Thermal Conductivity[1] ~8X Reduction  Experimental structures Experimental structures Experimental results Experimental results [1] Yu et. al Nature Nanotech., 2010. Porous Silicon  an attractive alternative for RT thermoelectric material. How about porous SiNWs ? Porous Silicon  an attractive alternative for RT thermoelectric material. How about porous SiNWs ? 47
  • 48.
    Abhijeet Paul Electronic andPhonon dispersion: Porous SiNW Rh=0.4 nm Dsep=0.2 to 1 nm Hollow SiNW: [100], W=4nm Tight Binding Tight Binding Increase in Ec  more confinement More flat bands  Suppression of heat flow.MVFFMVFF Increased electron and phonon confinement in porous SiNWs compared to filled nanowire. Increased electron and phonon confinement in porous SiNWs compared to filled nanowire. 48
  • 49.
    Abhijeet Paul Electrical andthermal transport parameters  Landauer’s method with scattering Electrical and thermal transport parameters  Landauer’s method with scattering Electron and Phonon dispersionElectron and Phonon dispersion Porous SiNWs: Electronic and lattice contribution to ZT ~7% drop  ~35% drop  T )( GS ZT l 2    e Thermoelectric Efficiency Thermoelectric Efficiency PF (S2 G) reduction ~49%  ~55% drop  kl reduction ~55%  Interplay of PF and κl determine the final ZT !!!Interplay of PF and κl determine the final ZT !!! 49 Solid nanowire
  • 50.
    Abhijeet Paul Porous SiNW:Power-factor and ZT ~49% drop  ~7% rise  Large reduction in Electrical power-factor due to pores. ZT improves due to large suppression on lattice thermal conductivity. ZT in porous SiNW improves but at the expense of electrical performance !!! ZT in porous SiNW improves but at the expense of electrical performance !!! 50
  • 51.
    Abhijeet Paul Conductance Measurement and simulations. Conductance Measurement andsimulations. Silicon nanowire Physical metrology How to determine size, shape and orientation ? Electrical metrology How to determine interface traps in SiNW FETs? Thermal properties How to determine thermal properties of SiNW ? Phonons  Lattice thermal properties Phonons  Lattice thermal properties Thermoelectricity How to enhance PF and ZT of SiNW ? Porous SiNW Enhance ZT Porous SiNW Enhance ZT Raman spectroscopy Phonon shift in SiNWs Raman spectroscopy Phonon shift in SiNWs Integrated modeling approach sheds light on many nano-scale aspects of SiNWs. Integrated modeling approach sheds light on many nano-scale aspects of SiNWs. 51
  • 52.
    Abhijeet Paul Key newfindings and accomplishments • Developed two new interface trap metrology methods in Si trigated FinFETs. »Methods are complimentary and repeatable. (Published in JAP, 2011, IEEE EDL 2010, IEEE EDL 2009) • Correlated the shape and size of SiNWs to phonon shifts  guides Raman Spectroscopy. (Accepted in JAP 2011) • Strain engineering of lattice thermal conductivity and specific heat of SiNWs possible. (Published in APL, 2011) • Possibility of using porous SiNWs for enhanced ZT (~6% rise) at room temperature shown. 52
  • 53.
    Abhijeet Paul Outline ofthe talk • Motivation »Why the present work is important ? »Need for integrated atomistic simulation framework • Computational modeling and simulation approaches. • Application of the methods to Si nanowires (SiNWs). • Application to non-Si system  GaAs a quick look !! • Global dissemination of findings  nanoHUB.org • Summary • Future directions 53
  • 54.
    Abhijeet Paul GaAs nanostructures: Electronicand thermoelectric enhancement 54 SiNWSiNW GaAs [100]/(100) ~38% inc. in ION for 4% strain p-type. Integrated Modeling Approach Integrated Modeling ApproachGa GaAs NW 0% 2% 5% kl = 1W/m-K [1] ~10% inc. in ZT for tensile strain n-type [1] Martin et al, Nanoletters, 10, 2010 A. Paul et. al, IEEE Nano, 2011 A. Paul et. al, IEEE DRC, 2011 Integrated modeling performance enhancement of GaAs nanostructures. Integrated modeling performance enhancement of GaAs nanostructures.
  • 55.
    Abhijeet Paul Outline ofthe talk • Motivation »Why the present work is important ? »Need for integrated atomistic simulation framework • Computational modeling and simulation approaches. • Application of the methods to Si nanowires (SiNWs). • Application to non-Si system  GaAs a quick look !! • Global dissemination of findings  nanoHUB.org • Summary • Future directions 55
  • 56.
    Abhijeet Paul Global scientificoutreach using nanoHUB.org •C/C++ and Matlab based tools. •Enables research in electronic structure and thermoelectricity 56 Open research tool for fellow researchers !!! Open research tool for fellow researchers !!! BandStructure Lab LANTEST Tool Research Tools Most popular tool on nanoHUB. Over 3K users. Till now ran 34503 simulations. Has been cited 28 times in research.
  • 57.
    Abhijeet Paul Global semiconductoreducation using nanoHUB.org 57 Semiconductor Educational Tools Crystal Viewer Tool Periodic Potential lab • 6 C/C++ and MATLAB based semiconductor physics tools developed. •Used in EE305 (Semiconductor Introduction) at Purdue University  Users (last 12 months) = 887  Simulations (last 12 months) ~3K Enabled dissemination of device physics knowledge globally. Enabled dissemination of device physics knowledge globally.
  • 58.
    Abhijeet Paul Outline ofthe talk • Motivation »Why the present work is important ? »Need for integrated atomistic simulation framework • Computational modeling and simulation approaches. • Application of the methods to Si nanowires (SiNWs). • Application to non-Si system  GaAs a quick look !! • Global dissemination of findings  nanoHUB.org • Summary • Future directions 58
  • 59.
    Abhijeet Paul Summary • Anintegrated modeling approach developed to study nanoscale devices. • SiNWs : »Electrical metrology  trap extraction method. »Structural metrology  Raman spectroscopy  phonon shift »Thermal property tuning  Phonon confinement. »Thermoelectricity  Porosity control. 59
  • 60.
    Abhijeet Paul Summary • GaAs: »Compressivestrain and body scaling enhances ION of UTB p- FETs. »Tensile strain and orientation enhances ZT of GaAs nanowires. • Global outreach for research using nanoHUB.org. 60
  • 61.
    Abhijeet Paul Outline ofthe talk • Motivation »Why the present work is important ? »Need for integrated atomistic simulation framework • Computational modeling and simulation approaches. • Application of the methods to Si nanowires (SiNWs). • Application to non-Si system  GaAs a quick look !! • Global dissemination of findings  nanoHUB.org • Summary • Future directions 61
  • 62.
    Abhijeet Paul Future directions •Combining electrons and phonons for better eletro-thermal understanding in nano-scale devices. • Increased device to system level interaction for better design optimizations. 62 http://www.comsol.com/papers/6801/
  • 63.
    Abhijeet Paul Future directions •Inclusion of thermodynamics into phonon calculations. • Investigation of source to drain tunneling for performance evaluation of ultra-short MOSFETs. 63 Lattice thermal expansion Si bulk http://www.ioffe.ru/SVA/NSM/Semicond/Si
  • 64.
  • 65.
    Abhijeet Paul Appendix A •References for Acoustic phonon shift »Si-1/Si-2: T. Thonhauser et. al, PRB, 69, 2004. (T) »Si-3: Hepplestone et. al., APL, 87, 2005. (T) • References for Optical phonon shift: »Si-1: Hepplestone et. al., APL, 87, 2005. (T) »Si-2: K. Adu et. al, App. Phys. A, 85, 2006. (E) »Si-3: Sun et. al, PRB, 72, 2005. (T) »Si-4: Campbell et. Al, Solid State Comm., 58, 1986. (T) »Si-5: Zi et. Al, APL, 69, 1996. (T) »Si-6: Yang et. Al, Jour. Phys. Chem., 112, 2008. (E) »Si-7: Faraci et. Al, Journ. App. Phys., 109, 2011. (T) T = Theory , E = Expt. 65