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GaN Compound Semiconductors for Ultraviolet, Visible, and Terahertz PhotonicsProf. Can Bayram, Innovative COmpound semiconductoR Laboratory (ICORLAB)Assistant Professor, Department of Electrical and Computer Engineering,University of Illinois at Urbana-Champaign, IL, USA EMAIL: [email protected]

WEBPAGE: icorlab.ece.Illinois.edu

September 9, 20142nd International Conference and Exhibition on Lasers, Optics, and Photonics , Philadelphia, USA

COLLABORATORS:

M. Razeghi, *Center for Quantum Devices, Department of Electrical Engineering and Computer Science, Northwestern University, IL USA

S. Bedell, J. Kim, H. Park, C. Cheng, J. Ott, K. Reuter, and D. Sadana,*IBM Thomas J. Watson Research Center, NY, USA

C. Dimitrakopoulos,*Department of Chemical Engineering, University of Massachusetts, MA, USA

4

1) Gallium Nitride Photonics

2) Ultraviolet Technology

• Next Phase (i.e. hexagonal vs. cubic)

3) Visible Light Emitting Diodes

• Vertical Thinking (i.e. lateral vs. vertical)

4) Terahertz Technology

• Room-Temperature Operation

5) Conclusion

OUTLINE

5

LightingWater Disinfection

Data StorageBio-Agent Detection

Gallium Nitride PhotonicsApplications

PowermW W

ULTRAVIOLET VISIBLE TERAHERTZ

Cancer Detection

Concealed Weapons Detection

200 nm Wavelength 700 nm 300 µm360 nm

6

Wavevector

Energy

conduction band

valence band

III-V MaterialsConventional III-V Materials : As/P-based

Column III

Column V

Al P

Ga As

In Sb

Wavevector

Energy

INDIRECT

DIRECT

Column III

Column V

Al P

Ga As

In Sb

3.5 mm

0.5 mm

Bandgap~0.35 eV

valence band

conduction band

Bandgap~2.4 eV

Column III

Column V

Al P

Ga As

In Sb

InSb

AlP

Column III

Column V

Al P

Ga As

In Sb

PhD Thesis by Can Bayram (2011)http://www.ioffe.ru/SVA/NSM/

7

III-V MaterialsEmerging III-V Materials : N-based

Column III

Column V

Al P

Ga As

In Sb

Column III

Column V

N

Al P

Ga As

In Sb

In N

Ga N

Visible

Infrared

1700 nm

800 nm

Al

N

Al N

Ga

Ga N

In

Ultraviolet

400 nm

200 nm

PhD Thesis by Can Bayram (2011); http://www.ioffe.ru/SVA/NSM/

8








5) Conclusion

OUTLINE

Disinfection

9

4.45 eV = + -(278 nm)

E

EEhc /1240/

Ultraviolet TechnologyEngineering UV LEDs for E-coli Targetting (λ~280 nm)

Device Structure

(0001) Sapphire

350 nm AlN

1 mm n+-Al0.55Ga0.45N

100 nm n-Al0.45Ga0.55N

50 nm p-Al0.45Ga0.55N

50 nm p-GaN

Al0.85Ga0.15N/AlN SL

20 nm p-Al0.7Ga0.3NMulti-Quantum-Well

Buffer

N-ContactLayer

Substrate

P-ContactLayer

Targetting Emission Wavelength

WellPBarrierP

CE

VE

4.41 eV

WellgapE

0.15 eV

he EE

0.11

PE

eE

hE

(+)

(+)

CB

VB

eE

hEWELLL

PE (-)

CB

VB

WELLL

WellAlX

BarrierAlY

WELLL

BARRIERL

QU

AN

TU

MS

TAR

K

WellgapE (+) Well

gapE

CB

VB BU

LKVegard’s Law

)1()1()1( xxbExxEE GaNgap

AlNgap

NxAlxGagap

BARRIER: Al0.40Ga0.60N 10 nm

WELL:5 nm Al0.36Ga0.64N

BARRIER: Al0.40Ga0.60N 10 nm

Multi-Quantum-Well

250 300 350 400 450 500 550

E

L In

tens

ity (

a.u.

)

Wavelength (nm)

λ≈280 nm

-2 0 2 4 6 8 100

5

10

15

20

25

30

Von= 6.0 V

Rs = 25

Curr

ent (m

A)

Voltage (V)

Electroluminescence I-V Curve

36.0WellAlX

40.0BarrierAlY

nmLWELL 5

nmLBARRIER 10

DesignParameters

10

Ultraviolet TechnologyGermicidal Flashlights (λ~265, 280, 340 nm)

Near-Field Image

Packaged UV LED Die

UV Flashlights

300 m

80 80 mAmA, CW, CW

300 µm

Spectrum

15 c

m

Batte

ry

50 mm

250 300 350

EL Inte

nsi

ty (

a.u

.)

Wavelength (nm)

250 300 350

EL In

tensi

ty (a.u

.)

Wavelength (nm)

250 300 350

EL

Inte

nsity

(a.

u.)

Wavelength (nm)

250 300 350

EL In

tensi

ty (

a.u

.)

Wavelength (nm)

PhD Theses. Alireza Yasan (2006); Ryan McClintock (2007), Can Bayram (2011)

11

P spontaneous (PSP)

Ultraviolet TechnologyGoing Beyond Conventional LEDs: Understanding Polarization

Wurtzite Lattice Unit

At equilibrium

Ga

N

a

c

Tetrahedral Arrangement

Ga

N PSP

PSP

PSP

PSP

PSP

Al, Ga, In content

composition

Wurtzite Lattice UnitUnder stress

c'

a'

Stress Stress

Lattice & Thermal mismatch

stress

PPZ

Total Polarization (P) =

P piezoelectric (PPZ)+

Total Polarization (P) &

GaN

Polarization effects in semiconductors, Springer (2008)

12

LED UV-BLUE-GREEN RED

Material AlGaInN AlGaInAsP

Crystal Structure

Wurtzitehexagonal

Zincblendecubic

Polar Yes No

Substrate Insulating Conductive

LED Lateral Vertical

Ultraviolet TechnologyGoing Beyond Conventional LEDs: Droop-free Approach

Visible LEDs & Droop

Appl. Phys. Express 4, 012101, (2011); PhD Thesis by Won Seok Lee (2011); PhD Thesis by Can Bayram (2011); Appl. Phys. Lett. 102, 011106 (2013)

UV LED

BLUE LED

GREEN LED

DROOPRED LED

13

Ultraviolet TechnologyGoing Beyond Conventional LEDs: Polarization-free Emitters

Adv. Funct. Mater.. 24 (28) 4491(2014)

SiO

2

SiO

2

Si(100)

GaN

Novel U-PatterningGe

SiO

2

SiO

2

Si(100)

GaAs

SiO

2

SiO

2

Si(100)

14

SiO

2

SiO

2

Si(100)

GaN


MOCVD Process

Selective

Selective Single Crystal Single phase Controlled

XRD

Inte

nsi

ty (

a.u

.)

2Theta (o)

c-GaN(002)

Si(004)

40 50 60 70

XRD

Phase Boundaries GaN

Zincblendediffraction

Adv. Funct. Mater.. doi: 10.1002/adfm.201304062 (2014)

Novel U-Patterning

Silicondiffraction

Adv. Funct. Mater.. 24 (28) 4491(2014)

15

Going Polarization-Free

0 1 2 3 4 5 61E-6

1E-5

1E-4

1E-3

0.01

0.1

1

| e

and

h w

ave

func

tion

over

lap

|2

Well Thickness (nm)

Eliminating Polarization Conventional

wurtziteNew

zincblende


wurtzite zincblende

Stable YES YES

Stress TENSILE NONE

Crack YES NONE

Defect >1E9 cm-2 <1E8cm-2

E-Field MV/cm NONE

Cleave NO YES

Buffer Al 50% Al-free

Preliminary Demonstration

360 380 400 420 440 4600.0

0.2

0.4

0.6

0.8

1.0

PL I

nten

sity

(a.u

.)

Wavelength (nm)

GaN

MQW

Phase Boundaries

Silicon (100) subs.

SiO2 SiO2 SiO2

GaN

voidseam

Preliminary Demonstration

P

wurtzite

zincblende

Adv. Funct. Mater.. doi: 10.1002/adfm.201304062 (2014)Adv. Funct. Mater.. 24 (28) 4491(2014)

16








5) Conclusion

OUTLINE

Lighting

17

Conventional Novel

Architecture Lateral Vertical

Release Mechanism

Optical (Laser Liftoff)Chemical (Etch)

Mechanical (Stress)

Area mm2 substrate

Thickness 6 µm + subs. 300µm

<3 µm

Die Shape Square Custom

Flexible No Yes

Light Emitting DiodesVertical Thinking

http://www.photonics.com/

OpticalLaser Liftoff

MechanicalStress

LED stack

substrate(2-inch)

Cross-section Cross-section

UV Laser

mm2

(~1mm2)

Adv. Funct. Mater. 18, 2673–2684 (2008); Advanced Energy Materials 3 (5), 566–571(2013) Applied Physics Express 6 (11), 112301 (2013)

Bending Stiffness (Thickness)3

Lateral Architecture

Vertical Architecture

contact

contact contact

contact

currentcrowding

Cross-section Cross-section

light light

18

A Failure MechanismStress-guided Chipping

opening shear

Mechanical Releasestressor

Light Emitting DiodesMechanical Stress & Release: Novel Means for Thin-film Devices

Photograph of 4-inch Flexible Ge/InGaAs/InGaP Solar Cell

J-V characteristics

SO

LAR

CE

LLS THIN

FILM

BULK

Highest Specific Power ~ 2000 W/kg

LED

sPhotograph of 2-inch

(In)GaN-based Thin Film LEDElectroluminescence

THIN FILM

BULK

Largest Area Thin-film LEDs~ 75 cm2

Advanced Energy Materials 3 (5), 566–571 (2013);Applied Physics Express 6 (11), 112301 (2013)

19

Light Emitting DiodesA Revolutionary Strategy for GaN Devices

IN PRESSC. Bayram, J. Kim et. al.

Principle of direct van der Waals epitaxy of single-crystalline films on epitaxial graphene

Nature Communications. IN PRESS (2014)

20

SiC

Graphitization of SiC

Graphene

GaN

SiC

Epitaxy of GaN on graphene

GaNSiC

Ni

Ni stressor deposition

GaN

SiC

Ni Graphene

Tape

Layer release

Graphene/SiC

Return for reuseTransfer on arbitrary substrate

GaNNi

Silicon

Tape

Removal of tape and Ni

GaNSilicon

Light Emitting DiodesA Revolutionary Strategy: GaN on Graphene for Thin Film Devices

Graphene


21

Light Emitting DiodesRelease & Reuse Through Graphene Cleave Layer

Raman Spectra

Transfer

GaN Epitaxy Ni stressor

Mechanical Release

tape

released GaN on Ni

host substrate

3 µm

RMS roughness ~3 Å

1 µm

GaN on Insulator

REUSE

Fresh Reused


22

Light Emitting DiodesA Novel Application: Thin-film Blue LEDs

Structure Active Area

350 400 450 500 550 600

Inte

nsity

(a.

u.)

Wavelength (nm)

1 cm

PhotoluminescenceX-ray Diffraction

simulation

experiment

-2 0 2 4 6 8 10

0

5

10

15

Curr

ent (m

A)

Voltage (V)

I-V Curve

350 400 450 500 550 600

Inte

nsity

(a.

u.)

Wavelength (nm)

Electroluminescence

at10 mA

p-contact

n-contact

light

1 µm 100 nm


23








5) Conclusion

OUTLINE

Concealed Weapons Detection

24

• Intersubband transitions are three orders of magnitude faster

than interband ones.

• Material systems in near-infarred

• AlAs/InGaAs

• AlAsSb/InGaAs

• BeTe/ZnSe

• AlN/GaN SLs posses

• large conduction bandoffset (~2.1 eV)

• large LO phonon energy (~90 meV)

• large electron effective mass (0.2×m0)

Intersubband transition

Interband transition

• Very well thin widths

• Picosecond transitions

•Tunibility in a wide range

• RT operation

•Femtosecond transitions

CB

Transition speed in• AlGaN is ~ 100 femtosecond vs. InGaAs is ~1-10 picosecond.

Required width of• (Al)GaN well is ~ 8 ML vs InGaAs well is ~ 2 ML

VB

Comparison: GaAs vs. GaN for 1.55 µm

devices

GaN-based Intersubband DevicesMotivation

25

High Al Content

Low Al Content

Bayram C. J. Appl. Phys. 111, 013514 (2012); Bayram et al. Appl. Phys. Lett. 95, 131109 (2009); Bayram et al. Appl. Phys. Lett. 95, 201906 (2009).

Infrared TechnologyWorld’s First GaN-based Infrared Devices

Active Layer Structure Tunability in the Infrared via Al-content

•First GaN-based infrared devices:

•Shortest wavelength: 1.0 µm (by MOCVD)

•Longest wavelength: 5.3 µm

26

Resonant Tunneling DiodesWorld’s First GaN-based Reliable and Reproducible RTDs

0 2 4 6 80

2

4

6

8

10

300 K C

urr

ent

Den

sity

(kA

/cm

2 )

Voltage (V)

77 K

•First GaN-based resonant tunneling diodes:

•Reproducible I-V curves;•Tunneling at room and low

temperatures.

Device Structure Negative Resistance in RT and 77 K

THz Oscillators Quantum Devices

doping

Injector

doping

Injector

ActiveRegion

Bayram et al. Appl. Phys. Lett. 97, 181109 (2010)

27

• GaN can have global impact through

• Ultraviolet light source with germicidal effects.

• Visible light sources for general illumination.

• Terahertz emitters operating at room temperature.

Summary

• Vertical thinking is critical for enabling innovative

and

exciting opportunities for GaN devices

• Polarization-free design

• Vertical architecture

Nature Nanotechnology. Under External Referee Review (2014)Adv. Funct. Mater.. doi: 10.1002/adfm.201304062 (2014)

PhD Thesis. Can Bayram (2011)

Si(100)

SiO

2

SiO

2

28

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