simulations in the development process of gan …focs.eng.uci.edu/papers for gan/general information...

Dominik Eisert21.10.02 Seite: 1

Simulations in the Development Processof GaN-based LEDs and Laser Diodes

Dominik Eisert and Volker Härle



Introduction

InGaN

Light Emitting

Diodes

InGaN

Laser Diodes

• Applications for InGaN high brightness LEDs

• LED development process: where can simulations be useful?

• Specific InGaN chip development project accompanied by simulations

• Progress of Laser Diode Development at Osram OS


Our Activities and Locations

San Jose- BU OLED- Sales NA

Tokyo- Sales Japan

Singapore- Sales Asia Pacific

Penang- Backend Plant- OLEDFrontend

Wuxi- Backend Plant (Subcon Infineon)

Regensburg- Headquarter- Sales- BU LED- BU Infrared/Power Laser- BU Lamp Modules- Technology- Frontend Production

Villach- Silicon Waferfab (Subcon Infineon)

Siemens AG → OSRAM GmbH → OSRAM Opto Semiconductors GmbH


World Market by Product Segments

80801050

210880

95200

1180

275

990

115655

1320

340

1110

150

1060

1455

415

1240

195

1510

1610

485

1360

260

1825

1750

535

1480

305

2255

2000

650

1790

2300

3540

5850

51604320

2740

Source: OSRAM OS

Mill. Euro Mill. Euro VIS

VIS Aut

IR/HPL

OLED/ID

LM

99/00 00/01 01/02 02/03 03/04 04/05 05/06

19 %

13 %

31 %

12 %

150 %

19 %

29 %

12 %

24 %

12 %

228 %

21 %

22 %

12 %

22 %

10 %

62 %

30 %

19 %

10 %

17 %

11 %

42 %

30 %

13 %

9 %

10 %

9 %

21 %

33 %

c.a.g.r. 20 %20 %

21 %

21 %

14 %

24 %

17 %

13 %

21 %

11 %

74 %

25%

7000


Material Systems for High Brightness LEDs

lattice parameter [Å]

band

gap

ener

gy [

eV]

wav

elen

gth

[nm

]

700600

500

400

AlN

1,0

1,5

2,0

2,5

3,0

3,5

4,0

2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,5

6,2

InGaAlP

InN

SiC

GaN

InPGaAs

GaP

AlP

InGaN


Applications for GaN-LEDs

Mobile ApplicationsAutomotive Interior + Exterior

Marker Lights


Applications for LED Modules

Signal Lights

Illuminated Signs

Full Color Displays


Are Semiconductors the Light of the Future?

0

50

100

150

200

1970 1980 1990 2000 2010 2020

Ligh

t Sou

rce

Eff

icie

ncy

[lm/W

]102

103

104

105

1970 1980 1990 2000 2010 2020

Ene

rgy

Con

sum

ptio

n [T

Wh]

Electricity

1.2 x104 TWh

6.9 x104 TWh

Energy

Illumination2.3 x103 TWh

USA: 20% of electr.BRD: 8% of electr.

World Energy Consumption p.a.

Incandescent

Halogen

Fluorescent

Semi-conductor

projected

Source: R. Haitz, Hewlett-PackardSource: International Energy Agency

Efficiencies of Light Sources

with acceler.effort

projected1998


“White LED”

620

600

580

560

540

520

500

490

480

460

510

E

InGaN-chip generates blue light

partial conversionby a phosphore

color mixing⇒ WHITE

package

chipconverter


Lamp Modules Applications:General Lighting

LED Modules for general lighting• information and orientation lighting

• effect lighting

• ambient lighting

LED Modules offerscreative design possibilities

extremely low-profile light solutions

high light output ratio

reduced maintenance costs


Processes

Properties To Optimize

Parameters

Complexity of LED Production

Epitaxy

internal QE / gainmode control (LD)

voltage controldefects

growth kineticsMOVPE Reactor

Chip Processing

semiconductor processes

external QE (LED)mode control (LD)

voltage controlthermal management

Packaging

light extractionluminance

thermal managementmechanical properties

reliability

molding/castingmass production

Module

light distributionimagingcontrast

power drivers

systemintegration

heterostructure design

chip geometrycontacts

housing geometrypolymer materials

light guidesboard design


LED Development Scenario

ProductIdea

Moore‘sLaw

Competition

DesignConcept

DesignVerification

CustomerProductReliability

ProcessDevelopment

Optimization?

TIME+COST

EpitaxyChip

i++

Concept Proof Process PackageLogistics

Simulation Simulation

Qua

litity

Mar

ketin

g

Sem

icon

duct

orD

evel

opm

ent

Pac

kage

Dev

el.

SimulationInformation


0

1

2

3

4

5

6

Feb99

Mar99

Apr99

May99

Jun99

Jul99

Aug99

Sep99

Oct99

Nov99

Dec99

Jan00

po

wer

ou

tpu

t @

20m

A (

mW

)

0%

1%

2%

3%

4%

5%

6%

7%

8%

9%

10%

wal

lplu

g e

ffic

ien

cy

Brightness Development of InGaN QW-LED

Sapphire technology used by competitors

70µm

250µm

SiC-technologyfavored by Osram

deve

lopm

ent

of ep

itaxy

for 460nm blue LEDin 5mm Radial housing


„Dark“ Transparent Substrate?

GaP-based chip GaN on SiC

Though 6H-SiC is transparent for blue light: no emission from substrate observed!

GaP SiC

GaN

angulardistribution


Light Extraction from GaN/SiC-System

Transparent Substrate SiC (Eg=3.03eV) but n(GaN) < n(SiC)

Snell‘s law‚blind‘ angle (22°)

Light Extraction from SiC: θc=33°

n=1.5 n=2.7

θc

Incomplete Overlap ⇒ low efficiency

outcouplingangle (11°) ‚blind‘

angle

⇓GaN: n=2.5

SiC: n=2.7


How can the Efficiency be Improved

improved light extraction:

Increase overlap of incident rays with outcoupling cone

Inclined substratefacets

§ optimized use ofoutcoupling cone

§ light extraction on firstincidence


Steps towards Realization of ATON-Technology

standard cube: η=100%

first test: η=115%

‚proof‘ of design: η=145%

final ATON design: η=180%

dicing process modification: transfer of inclined facet design into SiC-substrate

• fewer experimental optimization cycles• confidence in optimum performance level

accompanied by simulation

Simulation:


Raytracing Analysis

X

Objectivel of Chip Development: • optimize External Quantum Efficiency (EQE)

EQE hard to assess experimentally!

Non-sequential Raytracing Analysis ⇒ EQE + intensity distribution

+ complete geometrical 3D chip model + transparent + absorbing elements + scattering + interface to package development

− wave effects − electrical/thermal properties


Optimization of Chip Shape

20

25

30

35

40

45

50

55

60

0 10 20 30 40 50 60 70 80 90Facet Angle (°)

Ext

ern

al Q

uan

tum

Eff

icie

ncy

(%

)

75µm100µm150µm

ATON footprint

Facet Angle

• optimum facet angle ≈30° ⇒ Doubling of Extraction Efficiency• limited by ohmic heating

ATON/socket ratio (290x290µm chip)

0

10

20

30

40

50

60

70

0 50 100 150 200

ATON footprint (µm)E

xter

nal

Qu

antu

m E

ffic

ien

cy (

%)

optical extraction efficiency

heating considered

ohmic heatgeneration


ATON in TOPLED - Package

Standard Chip

ATONChip

brightness gain from backwards directed radiation

⇒ REFLECTOR is essential!

0

30

60

90

120

150

180

210

240

270

300

3300

30

60

90

120

150

180

210

240

270

300

330


Reliability of ATON Chip in Package:Mechanical Stresses

thermoplast

metal

epoxyLED-Package:materials with largely differingthermal expansion coefficients⇒ Delamination?

FEA shows no increased delamination risks for pyramidal chip


Brightness Development of InGaN-LED

0

2

4

6

8

10

12

Feb 9

9

May 99

Aug 9

9

Nov 99

Feb 0

0

May 00

Aug 0

0Nov

00Fe

b 01

May 01

Aug 0

1

Nov 01

Feb 0

2

May 02

Aug 0

2

po

wer

ou

tpu

t B

LU

E 4

60n

m (

mW

)

0,0

0,5

1,0

1,5

2,0

lum

ino

us

flu

x W

HIT

E (

lm)

ATON-Technology

‚Flip‘-Chipreflectingp-contact

290µm Chipin package@If=20mA


0

10

20

30

40

50

60

200 400 600 800 1000

Chip Size (µm)

Ext

ern

al Q

uan

tum

Eff

icie

ncy

(%)

LEDs for POWER Applications

Applications like e.g. Headlamps • LEDs with high luminous flux

⇒ go to high operation currents (350mA, 1W)

• new low Rth package• increase chip size to minimize heating

Simulation shows: efficiency decreases with chip size!

0

5

10

15

20

25

30

0 20 40 60 80 100I (mA)

Phi

_e (

mW

)

DC

pulsed


High flux LED on SiC: Options for Scalability

Multiple inner grooves Surface texturing

• Φe= 150 mW blue Φv= 33 lm white• If=350 mA / Uf=3,9 V• Chip area: 1 mm2

0

5

10

15

20

25

30

35

40

45

50

0 100 200 300 400 500current (mA)

wh

ite

ligh

t P

hi_

v (l

m)

0

50

100

150

200

250

blu

e lig

ht

Ph

i_e

(mW

)

whiteblue


Potential Market Segments for Blue Laser Diodes

lighting

optical storage laser printing

medical technologyindustrial printing

technologyspectroscopy

...

projection - displays


Structure of InGaN Laser Diode on SiC

SiC-substrate

buffer

GaN:Mg

GaN:Mg

GaN:Si

AlGaN:Mg

AlGaN:Si

GaInN/GaN MQW

Vertical Structure

p-dopedcladding

n-dopedcladding

wave guideactive zone

contact layer

SiC

InGaN SCH-Laser Diode• SiC substrate• vertical current flow• ridge wave guide• cleaved facets• dielectric mirror coating


Work Packages with GaN Lasers on SiC

Indium fluctuations

Heterostructure design

CB

VBGaInN

Dislocations

lattice mismatch GaN/SiC 3.4%disloc. dens. up to 5x109cm2

epitaxial growth parameters

• number and depth of quantum wells• piezoelectric effect• wave guides

Reduction of Losses• p-contact• laser facets

• index guiding• laser mounting


Minimize Threshold Current Density

• optimum number of quantum wells: 2-3

• electrical confinement vs. - piezoelectric effect - Indium phase separation

395 400 405 415 420 425 430

20

30

40

50

60

Indium content

thre

shol

d cu

rren

t den

sity

(kA

/cm

²)

emission wavelength (nm)

quantum well width: ~ 2 nm

390 410 435 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,530

35

40

45

50

55

thre

shol

d cu

rren

t den

sity

(kA

/cm

²)

quantum well width (nm)

gain guided, no mirror coatings

quantum well parameters


Influence of Mounting

§ 3 µm ridge, heatspreader c-BN§ calculated thermal resistance Rth = 22.8 K/W

Direction of mounting:

→ not critical due to high thermal conductivity of SiC (=Cu)

0. 1. 2. 3. 4. 5. 6.

Y

e3

-2.

-1.

0.

1.

2.

3.

4.

CuW-heat sink

BN-heat spreaderlaser structure on SiC

C. Eichler, Univ. Ulmepi-side-up epi-side-down

Mounting Technology


Lasing Characteristics

0 50 100 150 2000

10

20

30

0

2

4

6

8

10

CW

Puls

Puls- & cw-KennlinienPuls CWIth = 89 mA 96 mA

jth = 5,4 kA/cm2 5,8 kA/cm2

η = 240 mW/A 191 mW/AU

th = 5,8 V 6,0 V

∆T = 10 KR

th = 18 K/W

I (mA)

U (V)P (mW)

0 100 200 300 400 5000

10

20

30

40

50

60

0

2

4

6

8

10

12

CW

60 mW cw optische Leistung

opt.

Leis

tung

(m

W)

cw-KenndatenI

th = 193 mA

jth = 11.7 kA/cm

2

η = 340 mW/AU

th = 7.4 V

Spa

nnun

g (V

)

I (mA)

U (V)P (mW)

facet reflectivity 16% - 98%

output power of 60mW

facet reflectivity 70% - 98%

threshold current 96mA


Lifetime Development

0,01

0,1

1

10

100

1000

Jul 01

Aug 0

1

Sep 0

1Okt 0

1

Nov 01

Dez 01

Jan 0

2

Feb 0

2Mrz

02Ap

r 02

Mai 02

Jun 0

2Ju

l 02

life

tim

e cw

@ 1

mW

[h

]

143h

ridge: 2.7x600µm

Rth: 18K/W

Ithr: 96mA

Uthr: 6V

Pel: 0.6W

Tpn: 35°C

Actual values

life time 143 h @ 1mW 54h @10mW

(first pulsed LD: 07/99 first cw LD: 03/01)


Lifetime of GaN Laser Diodes: Defect Density and Pump Power

1

10

100

1000

10000

100000

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8

electr. power dissipation [W]

lifet

ime

[h]

Sony (on sapphire) - EPD: 3x10(exp8) 1/cm²

Sony (on ELO-GaN) - EPD: 1x10(exp5) 1/cm²

Nichia (HVPE) - EPD: 5x10(exp7) 1/cm²

Nichia (ELO) - EPD: 1x 10(exp6) 1/cm²

Nichia ( HVPE & ELO) - EPD: 7x10(exp5) 1/cm²

OSRAM OS (on SiC) - EPD: 3x10(exp9) 1/cm²

influence of reduced

dislocation density

lifetime limiting factor: Pel > 1W: Pel Pel < 1W: defect density

lifetime >10000h: Pel < 0.4W defect density ≤ 1x106 cm-2



ATON LED-Technology

Simulations inDevelopment

Benefit ofSimulations

InGaN LaserDiodes

Thanks

• 80% brightness improvement• makes SiC-technology highly competitive

• extensive use of Raytracing Simulations chip optimization, emission patterns, ...

• fast and linear progress• know-how basis for future projects

• life time of 143h optimizing GaN on SiC technology• next objective must be defect reduction

InGaN LED/LD devel. team, Process devel. groupPackage devel. group, External partners

simulations in the development process of gan …focs.eng.uci.edu/papers for gan/general information...

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