Full-band Simulations of Band-to-Band Tunneling Diodes Woo-Suhl Cho, Mathieu Luisier and Gerhard Klimeck Purdue University Investigate the performance of homogeneous InGaAs and broken gap GaSb-InAs III-V band-to-band-tunneling (BTBT) diodes Study the tunneling properties of a given material and its potential as a BTBT Field-Effect Transistors (FETs) Use full-band and atomistic quantum transport solver based on tight-binding to simulate BTBT diodes Coherent tunneling (no e-ph) Compare the simulation results to experimental data from Notre Dame and Penn State Good agreement with experimental data for the Zener tunneling branch Poor agreement in the negative differential resistance (NDR) regime: peak, valley, and thermionic currents not well captured Solution: band gap narrowing and e-ph scattering Proper modeling of band gap narrowing as function of doping concentrations Verification of thermionic current with drift-diffusion solver Solve convergence problem for GaSb-InAs broken gap diodes OBJECTIVE RESULTS APPROACH ONGOING WORKS III-V Band-to-band tunneling (BTBT) diodes Fabricate and measure tunneling currents in 1-D TD (Notre Dame (A) , Penn State (B) and MIND Partners) Homogeneous material: (A) InGaAs Broken gap heterostructure: (B) AlGaSb-InAs Use full band and atomistic quantum transport simulator based on the tight-binding model (OMEN) Solve NEGF using recursive Green’s function algorithm Reproduce experimental data (A) (B) Approach Physical Models Device Engineering Efficient Parallel Computing 3D Quantum Transport Solver Accurate Representation of the Semiconductor Properties Atomistic Description of Devices Ballistic and Dissipative Explore, Understand, Explain, Optimize Novel Designs Predict Device Performances Predict Eventual Deficiencies Before Fabrication Accelerate Simulation Time Investigate New Phenomena at the Nanometer Scale Move Hero Experiments to a Day-to-Day Basis GAA NW Electron Density Id-Vgs Parallelization Scheme OMEN Multidisciplinary Effort: PHYS - EE - HPC 4 Simulation Structure Band Diagram In0.53Ga0.47As 20nm 10nm 3nm D (N+) S (P+) x EF 0.75eV P+ N+ InGaAs lattice matched to InP NA_S=8×1019/cm3, ND_S=106/cm3 ND_D=4×1019/m3, NA_D=106/m3 Heavily doped P-N Overlap between CB & VB Possibility of tunneling 1D TD: Homogeneous material 5 Motivation BTBT FET BTBT Diode Buried Oxide P+ N+ Gate oxide S D I Gate P+ drain N+ source Substrate Promising device No low limit on the SS Low power consumption Horizontal structure Difficult to get sharp interface Need excellent channel control through gate Vertical structure No need for sharp interface or gate control Good to learn about the tunneling properties Good to test the potential of a given material as a TFET Experimental data exist 1 2 3 Only Zener tunneling branch is shown Better match to experimental data with step-like junction 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 V [V] X106 I [A/cm2] In0.53Ga0.47As TD Penn State (S. Datta) Influence of p-n junction profile Comparison to Experimental Data 6 Step junction is used Zener current matched Poor reproduction of NDR region low peak and valley currents No electron-phonon scattering valley current cannot be matched Investigate potential explanations for the observed misbehavior Complete I-V Characteristics: Simulation vs Experiment 7 Higher peak current, no change in valley current No shift of the thermionic current EF-EC of drain ( ) varies due to donor doping No change for ( ) region P+ N+ EF (1) Variation of the donor concentration ND 8 Small increase of peak current, no change for valley Shift of the thermionic current turn-on EV-EF of source ( ) varies due to acceptor doping Change for ( ) region P+ N+ EF (2) Variation of the acceptor concentration NA 9 Study the effect of BGN through smaller band-gap material In0.53Ga0.47As with Eg=0.7511 (eV) vs In0.75Ga0.25As with Eg=0.5444 (eV) Increase of peak and valley tunneling current + shift of thermionic current branch (3) Band Gap Narrowing (BGN) 10 Modeling Compute CB and VB shift as function of doping concentrations Model TD as heterostructure with 2 different materials Goals: increase of peak current and shift of thermionic current 20nm 10nm S D x In0.53Ga0.47As after BGN 0.75eV In0.53Ga0.47As before BGN Solution: accurate modeling of BGN 11 OMEN: Quantum transport simulator based on tight-binding model PADRE: A device simulator using drift-diffusion Corrected values of NV and NC based on the results of OMEN used Shows ideal IV curve for a PN diode and where the thermionic current starts More thermionic current shift with PADRE 12 10 8 6 4 2 -2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Voltage [V] X 105 I [A/cm2] Comparison to drift-diffusion simulations Simulation Structure Band Diagram GaSb (P+) InAs(N+) EF 0.751eV 0.37eV S D InAs (N+) 25nm 50nm 2nm x NA_S=1019/cm3, ND_S=106/cm3 ND_D=2×1018/cm3, NA_D=106/cm3 Lattice matched a=0.60959 nm at 300K Broken gap High tunneling current 1D TD: Heterostructure with broken gap 13 Poisson Convergence Problem Accurate modeling of BGN in InGaAs TD BGN can be calculated from Jain-Roulston model Verification of thermionic current turn-on No tunneling required direct comparison to drift-diffusion possible Convergence problem with Poisson equation in broken gap heterostructure Simplest solution: fictitious scattering through imaginary potential (parameter sensitivity?) Ongoing work 15 Tunneling current through Broken gap material Problem with hole accumulation on the p-side Electron-phonon scattering needed to fill these states Cannot fill the states InAs (N+) D GaSb (P+) S e 14