Full-band Simulations of Band-to-Band Tunneling DiodesWoo-Suhl Cho, Mathieu Luisier and Gerhard Klimeck

Purdue University

• 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)

ApproachBTBT Diode

P+ drain

N+ source

SubstrateBuried Oxide

P+ N+

Gate oxide

S DI

Gate

• 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

MotivationBTBT FET

• 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

Physical ModelsDevice 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

ElectronDensity

Id-Vgs

Para

lleliz

atio

n

Scheme

OMEN

Multidisciplinary Effort: PHYS - EE - HPC

4

• 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

00 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

/cm

2]

In0.53Ga0.47As TDPenn State (S. Datta)

Influence of p-n junction profile

Comparison to Experimental Data

6

1

Simulation Structure Band Diagram

In0.53Ga0.47As

20nm

10nm

3nm

D (N+)

S (P+)x

In0.53Ga0.47As

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

• 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

• 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

0

-20 0.2 0.4 0.6 0.8 1 1.2 1.4 Voltage [V]

X 105

I [A

/cm

2]

Comparison to drift-diffusion simulations

12

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

20nm10nm

S D

x

In0.53Ga0.47As after BGN

0.75eV

20nm10nm

S D

x

In0.53Ga0.47As before BGN

0.75eV

Solution: accurate modeling of BGN

11

Simulation Structure Band Diagram

GaSb (P+)

InAs(N+)

EF

0.751eV

0.37eV

S

DInAs (N+)

GaSb (P+)25nm

50nm

2nm

S

D 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

• 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

Cannot fill the states

InAs (N+)

DGaSb (P+)

S

ee

• Tunneling current through Broken gap material- Problem with hole accumulation on the p-side- Electron-phonon scattering needed to fill these

states

Poisson Convergence Problem

14

• 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

• 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)

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2 3