duv nitride leds - challenges and perspectives

8/16/2019 DUV Nitride LEDs - Challenges and Perspectives

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Nikkiso Giken Co.,Ltd

October 15 – 17, 2014

Pacifico Yokohama -Yokohama, Japan

www.sil-ledjapan.com

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DUV Nitride LEDs:

－ Challenges and Perspectives －

Cyril PernotManager, Hakusan Factory, Crystal Growth Section

NIKKISO CO.,LTD


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Presentation Outline

1. Introduction: Generality about UV-LED

2. Challenges for DUV-LED Substrates Layer structure, Layer doping

Life time Package

3. Perspectives for DUV-LED Advantages of DUV-LED Toward Higher Irradiance Applications for DUV-LED

Existing and New Market

4. Conclusion


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Band Gap Energy and Wavelength

Ultraviolet radiation range (ISO standard): 315nm～400nm・・・UVA

280nm～315nm・・・UVB 100nm～280nm・・・UVC

DUV (Deep Ultra Violet) refers to wavelength below 300nm

0.0

0.5

1.0

250 300 350 400

Wavelength [nm]

N o r m a l i z

e d I n t e n s i t y [ a . u . ] 255nm

270nm

280nm

290nm

305nm

315nm

335nm

350nm

Introduction

AlGaN-based UV LED


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TO-46 Type UV-LED

Unit 265nm 285nm 300nm

Rated Current IF mA 15 20 20

Forward Voltage Vf V 5.5～7.5 4.5～6 45～6

Power PO mW ＞ 3 ＞ 1 ＞ 1

Peak wavelength λP nm 265±5 285±5 300±5

FWHM Δλ nm ＜15 ＜15 ＜20

Directivity 2θ1/2 deg. 80 80 80

Item

Specifications

Market Available DUV-LED

8.0mm sq PKG. 8.0mm sq PKGon PWB substrate.

Unit 265nm 285nm 300nm

Rated Current IF mA 100 100 100

Forward Voltage Vf V 5 ～7 4 .5 ～6 .5 4.5 ～6 .5

Power PO mW ＞ 4 ＞ 1 ＞ 1

Peak wavelength λP nm 265±5 285±5 300±5

FWHM Δλ nm ＜15 ＜15 ＜20

Directivity 2θ1/2 deg. 130 130 130

Item

Specifications

SMD Type UV-LED

Introduction

NIKKISO CO., LTD. NIKKISO CO., LTD.


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Parameters for LED die characterizationIntroduction

EQE = IQE x LEEWPE = EQE x EE

Parameter Blue LED(InGaN-based)

DUV LED(AlGaN-based)

IQE: Internal Quantum Efficiency >80% 80% 80% 70% 50% 3mm)

>5 W

( >5 W/cm2

)

< 100 mW

( 10000 hours >1000 hours

Cost/ mW $ $$$

Comparison of Blue and DUV-LED


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Evolution of EQE of DUV-LED

2005

2013 (Michael Kneissl, TU Berlin (last updated 4-12-2013, HP)

• In less than 10 years, Performance

increased by one order in DUV range

Our Group data (2014 update) for bare chips

Introduction


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October 15 – 17, 2014



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Standard DUV LED Structure

TO / SMD

Substrate: AlN vs Sapphire

Light Extraction (patterning, chip shape,resin encapsulation, reflector)

Active region area and design(carrier injection, IQE, )

p-Layers(holes injection, UV transparency,reflective electrodes)

Thermal management (package, flip-chip)

nAlGaN Template:

(sheet and contact resistance)

Flip-Chip Configuration

AlN

Introduction



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Which Substrate ?

• Template will affect the crystal quality, the Al mole fraction and the stress of theovergrowth AlGaN layer

Approach Growth Method Crystal qual ity Growth Challenge DUV LED

EQE

Availabil it y

AlN onSapphire

-MEMOCVD-Pulse-flow-High Temp

-DD～109cm-2 -Smooth(DD: DislocationDensity)

Lattice mismatch,cracks

EQE 6.5%(>10% forimproved LEE)

Up to 4 inch (demonstrated)

ELO AlN -on Patterned Sa-on Patterned AlN

-DD



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Light emission efficiency and Dislocation DensityChallenges

Simulations of IQE for Blue LED: High defect density in AlGaN layers leads to

reduced radiative recombination efficiencies

For years performance of UV LED was limitedby lack of template with good crystal quality

“ An increase in the nonequilibrium carrier

concentration provides a higher efficiency viasaturation of the non-radiative recombinationchannel”.

=> For Threading Dislocation Density below109cm-2 we can expect to get IQE over 50%

0

0.5

1

1.5

2

2.5

3

3.5

4

4.55

300 400 500 600 700

(10-10) XRC FWHM

O u t p

u t P o w e r ( m W )

280-300 nm LEDs342 nm LED

342 nm LED on ELO

C. Pernot et al., PSS A 208, 7, 1594-1596(2011)

( a . u . )

Output power vs template crystal quality:



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The Active Region

From EQE measurement :

EQE = IQE x LEE => IQE = EQE(measured) / LEE (simulation)

For Flip-chip configuration (bare-chip), LEE estimation was reported by different group:• LEE (ray tracing): 6% => IQE ～25% (Shatalov, JAP 105, 073103, 2009)• LEE (simulation) < 9% => IQE～17% (J.R. Grandusky PSS C8, 5, 2011)• LEE 7～9%, M. Kneissl et al. Semicond. Sci. Technology 26 (2011) 01436• LEE 8%(estimation) => IQE = 65% for 280nm (our group at ICNS 2011)

By Evaluating the IQE of the LED, we can assess the quality of the active region

• For 300nm QW on uAlGaN (MBE with potential fluctuation) IQE～ 32%, Liao et al. APL98 081110,2011• For 280nm InAlGaN QW on nAlGaN, IQE～ 86% (32% for AlGaN QW), H.Hirayama, PSS A 206, 6, 2009• For 280nm QW on n-AlGaN TDD 2x108cm-2 IQE～ 60% , Shatalov et al. APEX5 (2012) 082101

• For QW 60%, J.R. Grandusky PSS C8, 5, 2011

From PL measurement Temperature dependence

Challenges



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Doping of AlGaN Layers

Doping affect the current injection efficiency.Highly resistive layers will affect WPE and will lead to current crowding.

n-doping Up to 70% AlGaN, n-type layers with sheet resistance below 60 Ω/□ can be fabricated.

p-doping

Low hole carrier concentration for high Al molar fraction Mg-doped AlGaN layers.

New dopants, Different Semiconductors, New approach…• p-AlGaN doping using CBr4, Kawanishi et al. Proceeding, ICNS (2011)• Hexagonal boron nitride (hBN) 2.3 Ohm cm, S. Majety et al. APL 100, 061121 (2012)• Use of short period superlattice, S. Nikkishin et al. JJAP 44 7221 (2005)

p-GaN layer is usually used in DUV LED

Challenges



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Light Extraction

Reflective electrodes on p-Layers how to avoid p-GaN absorption?

By using Mesh p-GaN contact layerImprovement in LEE by 1.27(x1.55 when combining withn-reflective electrodes.=> LEE ～ 15% )Voltage increase by 0.45V (20mA)Life slightly affected

By using very th in p-GaN contact layer

p-GaN thickness < 10nm (>65% transmission) => Power increased by 1.2 times(H. Hirayama, Proceeding ICNS2011)

By using p-AlGaN contact layerWith reflective electrodes, without p-GaN contact layer : LEE: 15% (->EQE increased by 1.7 times)Increase in voltage by 2 to 4V (H. Hirayama, phys. Status Solidi 2014)

Challenges



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Reliability : Life time

Temperature and driving current are affecting life time of the DUV-LED devicebut origin and mechanism of degradation are still unclear.

By growing high quality DUV-LED, life time over 10.000 hours can be achieved.

Accelerated test device performance:for 289 nm bare chip on TO-5 CAN at 100 mA (=> Tj estimation > 100℃)

EQE (Initial) = 5.9%EQE (800hours) = 5.2 %(measured at 100mA)

WPE(initial) = 4.7%WPE(800hours) = 4.2%

Challenges



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Package

Temperature is affecting device performance (Power, Efficiency, Life) Nikkiso DUV LED on sapphire shows similar thermal derating as LED on AlN substrate

By improving the thermal resistance between the LED junction and the heat-sink, higher

performance at high current can be achieved

※HP values

※ ※

Challenges

Evolution of Nikkiso Package thermal resistance:

18℃/W



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Encapsulation

To improve light extraction efficiency, resin for encapsulation is actively researchedIn addition to LEE, mechanical and electrical reliability can be improved

Resin materials should present: Good transparency to DUV radiation Low degradation when exposed to UV light Refractive index between Air and Sa (AlN) Good adherence to the chip

Robustness to environment (not too soft) Half-ball shaping for efficient light extraction

LEE x 1.2 for 290nm LED on Sa, low degradation even for 256nm, our group IWN2012LEE x 2 for 270 nm LED on thinned AlN, J.R.Grandusky et al. APEX6 (2013) 032101LEE x 1.35 for 278nm LED on Sa, M.Shatalov et al. APEX5 (2012) 082101

Inazu et al. Spring Oyobutsuri Conf. 2011

Challenges

Ch ll



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Lower CostChallenges

The Cost per Watt of UV LED systems will come down as we get:

Volume production⇒ Higher demand (Specifications fitting the customers needs)

Lower fabrication Cost⇒ Cheaper substrates (Sa, larger diameter), dedicated facilities,

stable process, cheaper package solution (resin encapsulation)

Better Performance⇒ Higher Power (improved chip, improved package)

Higher Yield⇒ Dedicated and stable production systems

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Advantages of UV LED Systems

UV-LED Systems Benefits: Shock resistant semiconductor Customizable emission wavelength Easy integration (design flexibility, simple driving circuits, low voltage operation) Instant on/off => No warm-up/cool-down cycles, No shutter needed Diode Life time in excess of 10,000 hours

Consistent UV output over time No mercury-filled UV bulbs No ozone production => No system exhaust Lower total cost of ownership

By the Minamata Convention on Mercury, regulation on mercury will be strict from 2020.LED has low environmental impact, and has the potential to replace mercury lamps.

Perspectives

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Specification achievement of DUV-LED Die

EQE = 6.5% @ 10mAWPE = 5.0 % @ 10mA⇒ EE = 75%

Assuming LEE of 10%⇒ IQE ～ 65%

I-V Curve of UV-B LED

UVB LEDForward operating voltage at 100mA: 5.4VDiode resistance～4 ΩUVC LEDForward operating voltage at 100mA: 5.8VDiode resistance～7 Ω

Perspectives

289nm bare chip (2013)

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DUV-LED Irradiance evolution and target

To target High Irradiance we need to focus on Light Extraction Efficiency and on High Current operation

E Q E ( %

)

Year

Mid-Term Target

Long-Term Target

E Q E ( % ) , I r r a d i a n

c e ( m W / c m 2 )

Package andModule designImprovement

Higher current operation,High density packaging

Best data expected bycombining the best of thecurrent technology

Perspectives

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DUV-LED Package and Module Development

Optical Analysis Result:

*Uniformi ty of Irradiance : under 10% for the peak irradiance.

UV-LED Package

324pcs

λp:285nm

IN

OUT

SubstrateCu

Peak Wave le ngth Wo rk Distan ce I rradian ce Unif ormity o f irradian ce

265nm 3mm

57mW cm

2

5 mmsq

285nm 3mm

1 4mW cm

2

5 mmsq

3 nm 3mm

1 4mW cm

2

5 mmsq

Optical Analysis, WD : 3mm

Thermal

conduction greaseWater

cooling jacket

Perspectives

3.5mm sq Package

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High Density Packaging (Demo)

12x9 mm2 Air-cooling Module12 Chips

36mW/Chip @ 250mA

Voltage 71.58 V

Current 500 mA

Input Power 35.79 W

Output Power 728 mW

Irradiance 403 mW/cm2

Working Distance = 1mm Working Distance = 3mm

0

100

200

300

400

500

0 50 100 150 200 250 300 350 400 450 500

LED電流(mA)

光出力 ( m W / c m ^ 2 )

0

10

20

30

40

50

60

70

80

温度 ( ℃ )

放射照度

サブマウント温度

Current (mA)

O u t p u t P o w e r ( m W / c m 2 )

S u b M o un t t em p er a t ur e (

℃ )

Increasing chip densityImproving thermal resistivity

cooling (water cooling)

Irradiance of 500mW/cm2

Perspectives

Perspectives



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DUV-LED ApplicationsPerspectives

Replacement of existing UV light source → High Power, Low Cost New Applications specific to DUV LED → Time for final product development

Perspectives



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DUV-LED for Sensing Application

Technology Type Area Usage

Photo-absorption Type

Medical Dialysis Dose Monitor (DDM)Blood analysis device.

Food ManufacturingMeasurement of amount of enzymereaction.

Water QualityMeasurement

Measurements of hypochlorite,enzyme reaction and COD.

C om

p a c t

Original Light Strength【L0】

Weakened Light after Absorption. 【L1】

Light Source

Light Detecting Element

Sample

Electric Signal

Light Absorption

a. Compact and light weight.b. No need for optical filter.c. Easy to control (Instant start ,

Pulse lighting)d. Mercury freee. Wavelength is adjustable.

Perspectives

Perspectives


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285nm

DUV-LED for Sensing Application

What is DDM?

Dialysis Dose Monitor → DDM. Measurement of uric acid concentration contained in dialysis waste fluid

Uric acid is measured by absorption spectroscopy with UV-LED as light source

複式ポンプ

除水ポンプ

透析量モニタ

透析排液

C0’→C1’

相関性の高い物質の濃度変化をモニタリング

ダイアライザー

血液ポンプ

BUNC0→C1

Pump

Blood Pump

D.D.M.

Pump Monitoring for Uric Acid

Dialyzer

Dialysis Waste Fluid

λ:285nm

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Perspectives

Perspectives


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Sterilization by DUV-LED

BacterialBacillus substills, NBRC3134

(a) 265nm UVLED

before irradiation

(b) 285nm UVLED

before irradiation 540sec in irradiation time

UV-LED Specifications:(a)Wavelength: 265nm

Lighting intensity: 1.33mW/cm2

(b)Wavelength: 285nmLighting intensity: 2.41mW/cm2

Irradiation distance: 10mm

106

105

104

103

102

101

100

v i a b l e b a c t e r i a l c o u n t ( N )

UV irradiation time (sec)

265nm, present work

285nm, present work

non-irradiation

non-irradiation

200 sec in ir radiation time

About 120sec.(99.9%) About 220sec.(99.9%)

By using DUV-LED module with irradiation over 100mW/cm2 we can expect the same results withinseconds or at longer working distance.

285nm LED are also a promising candidate for sterilization applications.

Perspectives

Perspectives


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UV Curing

Jennifer Heathcote © 2013 RadTech International.

Stages for adoption of UV-LED in the curing industries

Perspectives

Perspectives


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UV Curing

・Higher absorbance at Short wavelength・Short wavelength would improve curing efficiency.

Perspectives

Perspectives


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Sterilization

UV-LED Applications Map

100

10

1

0

200 225 275250 350325300 375 400

Organic

decompositionWaste Water treatment

Wavelength (nm)

I r r a d i a n c e ( m W

/ c m 2 )

Low PressureMercury Lamp

254nm

Ozone

production

Sensing

DDM Application

Curing Application

PhotocatalystUnder385nm Air Purification, Sterilization,Deodorizing

SemiconductorDevelopment436nm

Phototherapy308nm

High PressureMercury Lamp

365nm

NIKKISOProductsTarget

Perspectives

Perspectives


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Prediction for UV-LED MarketPerspectives

For UVA range, UV-LED has already reached irradiance of >5 W/cm2

@ 385nm competingwith conventional light source => Current UV LED market is dominated by UVA LED (withwavelength >365nm)

For DUV-LED in addition to device specifications (wavelength, EQE) related to layer structureand quality, chip/package/module design will strongly affect the maximum irradiance and thereliability.

UV-LED module has to be low cost to compete with Hg lamp system

Source UV LED repor t, March 2013, Yole Developpement

Market size (M$)

UV LED market$45.0M12.7%

Traditional UV

lamp market$309.4M87.3% UV LED market

$299.1M37.1%

Traditional UV

lamp market$507.0M62.9%

UV LEDs


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Conclusion

• DUV-LED has some clear advantage compared with traditional UV light

source

• Large potential market for DUV LED : Need close collaboration withcustomers to develop appropriate module solutions.

• Significant improvement in the DUV-LED performance recently: moredevelopment is needed not only in the LED-chip performance but also inarrays, cooling and optics

• DUV-LED systems has to be Low cost to compete with Hg Lamp system

Thank you for your attention !

duv nitride leds - challenges and perspectives

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