Improving Deep UV LED Performance - SEMIsemi.org.cn/semiconchina/mail/160331/1/02-SEMICON... ·...

LED China Conference 2016, Shanghai, March 16th, 2016 1 Nikkiso Giken Co.,Ltd

Copyright © 2016 NIKKISO CO., LTD .All rights reserved.

Cyril Pernot – Manager, Development Department

March 16th, 2016

Improving Deep UV LED Performance LED China Conference 2016, Shanghai

NIKKISO GIKEN Co. Ltd.

Division



NIKKISO business Fields



Outline

1- Introduction: Going to shorter wavelength

2- Challenges and Performance of DUV-LED

3- DUV-LED Products Range and Applications

4- Conclusion



Wide range of Applications in UV



UV-LEDs are promising UV Sources


Copyright © 2016 NIKKISO CO., LTD .All rights reserved. 6

UV-LED Systems have many advantages

Integration

Operation

Environmental Impact

small size

robust

simple driving circuit

low voltage operation

Customizable emission wavelength

Instant On/Off

Modulation of UV output power

Low degradation, long life time

No ozone production

No mercury-filled UV bulbs



From Blue to UV LED



Nikkiso in UV-LED Business since 10 years

2006: UV Craftory, Nikkiso’s subsidiary established to develop and manufacture

DUV LED, based on Prof. Akasaki’s and Prof. Amano’s technology 2010: State-of-the-art results for UVC-LED (EQE > 3%)

2012: Starting sales of DUV-LED (mW level TO-can package)

2014: Nikkiso Giken becomes in charge of R&D, production and sales of UV-LED

2015: Nikkiso Hakusan Factory certified ISO9001:2008

Series production of 30 mW high power SMD product

2016: Series production of 50 mW high power SMD product



DUV-LEDs are based on AlGaN ternary alloy

By changing AlN mole fraction,

possible to tune the emission

wavelength

Difference in lattice parameter => stress, cracks, dislocations

GaN is absorbing wavelength

below 365nm.



DUV-LEDs have specifics challenges

Package

Sapphire

GaN

n-GaN

Active region

EB

p-GaN

Light output

InGaN-based LED : AlGaN-based DUV-LED :

Package

AlN



LEE is significantly affecting DUV-LED Performance

※ Best values are greatly depending on the measurement conditions and on the overall performance.

Parameters UV-LED

(InGaN-based)

DUV-LED

(AlGaN-based)

IQE: Internal Quantum Efficiency >80% <80%

LEE: Light extraction Efficiency >80% <25%

EQE: External Quantum Efficiency >80% <15%

EE: Electrical Efficiency >90% <90%

WPE: Wall Plug Efficiency >50% <5%

Max Power /Chip

(Irradiance Working Distance >3mm)

>5 W

( >16 W/cm2)

< 100 mW

(<500 mW/cm2)

Lifetime and reliability > 50000 hours >10000 hours

Cost/ W $ $$$$



Challenge for p-type doping

H. Amano et al. Proc. Of SPIE Vol. 7216 (2009)

Current DUV-LED devices are using :

・ thin pAlGaN layers for p-clad, and

・ pGaN for contact layer.

・New dopants, short period super lattice, different semiconductors, new

approach are under investigations for improving p-type layers.



Challenge for n-type doping

・n-type AlN very resistive

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

1.0E-04

1.0E-03

1.0E-02

1.0E-01

840 860 880 900 920 940 960 980

Co

nta

ct r

esi

tiv

ity

(a

rb.u

nit

)

Anneal temperature (degreeC)

Al：65%

Al：61%

Al：55%

High Al Content

Inazu et al. Autumn Oyobutsuri Conf. 2015



DUV-LED with low forward voltage

285nm DUV-LED :

=> Electrical efficiency over 90% can be achieved



High IQE by improving template quality

EQE Limit for

LEE of 10 %

Best EQE results obtained at low current

=> presence of droop at high current

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

300 400 500 600 700

(10-10) XRC FWHM

Ou

tpu

t P

ow

er

(mW

)

280-300 nm LEDs

342 nm LED

342 nm LED on ELO

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



Approach Crystal quality Growth Challenge DUV LED

EQE

Availability

AlN on flat

Sapphire

-DD～109cm-2 (DD: Dislocation Density)

Lattice mismatch,

cracks

EQE 6.5%

(>10% for

improved LEE)

Up to 4 inch (demonstrated)

ELO AlN (Epitaxial Lateral

Overgrowth)

-DD<2x108cm-2

Need regrowth, and

thick layer ,

coalescence difficult

(pits)

EQE 3% Difficult for large diameter,

Cost (need process, regrowth,

thick layer growth)

Bulk AlN -DD<105cm-2 UV Transparent

Layer, Low Al%

AlGaN regrowth

EQE 4%

(>7% for

improved LEE)

1 inch available (high cost),

2 inch (R&D stage)

Approaches for AlN Template Fabrication

⇒ Growth of DUV-LED on sapphire remains the competitive approach



EQE is decreasing at shorter wavelength

Maximum EQE of DUV-LED bare chip as a function of wavelength:

Issues for short wavelength emission:

- Carrier injection efficiency

- Polarization of light



High internal reflection and absorption

Internal refractive critical angle: αc = na/ns

ns

na

＊

Typical LEE for DUV-LED bare chip: 8～10%

n-layer

Active region

p-Layer



LEE Optimization (1) : Surface Roughening

C Pernot et al. Appl. Phys. Express 3 (2010) 061004

On wafer measurement

・Sapphire substrate with Moth-eye

pattern:

→On wafer Output Power ×1.5

Inoue et al. Appl. Phys. Lett. 106, 131104 (2015)

・ AlN substrate with

Hybrid nano photonic pattern

→Chip Output Power×1.96



LEE Optimization (2): Reflective Electrodes

Inazu et al. J. J. Appl. Phys. 50 (2011) 122101

・Mesh p-GaN contact layer with high reflective electrodes

Output Power x 1.27 (x1.55 when combining with n-reflective electrodes).

Voltage increase by 0.45V (20mA)

=> Trade-off between LEE improvement and Vf increase



LEE Improvement (3): Encapsulation

To improve light extraction efficiency, resin for encapsulation is actively researched

Good transparency

Low degradation

Good adherence to the chip

Half-ball shaping for efficient light extraction

Robustness to environment

Refractive index between Air and Sa (AlN)



Demonstration of over 100 mW at 275 nm

- Optimization of layer design

- Use of a UV-transparent encapsulant

Bare Chip

Chip with encapsulant

Single Chip Performance (R&D level)



DUV-LED Products and Characteristics

1 JPY coin

(20 mm)

【TO-46 CAN】



DUV-LED achieves Lifetime over 10000 hours

Temperature and driving current are affecting lifetime of the DUV-LED device

By growing high quality DUV-LED, lifetime over 10000 hours can be achieved.

Output power evolution for 285 nm DUV-LED:

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

10 100 1000 10000

Rel

ativ

e O

utp

ut

Po

wer

Time[h]

Driving Current：100mA (25℃)

00.10.20.30.40.50.60.70.80.9

11.1

10 100 1000 10000

Rel

ativ

e O

utp

ut

Po

wer

Time[h]

Driving Current：350mA (25℃)



Next Generation DUV LED reaches 50 mW

0

10

20

30

40

50

60

0 100 200 300 400

Ou

tpu

t P

ow

er

(mW

)

Forward Current (mA)

新規開発品

従来品

Ta = 25℃

Output Power x 1.7

Achievement of 50 mW at 350mA driving current

New LED

Standard LED



Optimization of Chip and Package design

⇒ By inserting reflective surfaces on the back side of the chip, it is possible

to limit absorption, and to improve the light extraction of the device

Highly

Reflective

Electrode

Package

Reflection Reflection

⇒ Improvement in Package Light extraction by using

highly reflecting material and shape

⇒ Increasing the contacting surface area between chip and package:

the thermal resistance 15 K/W => 9 K/W

nAlGaN

MQW

p-Layers

p-electrodes

AlN

Sapphire

n-electrodes

Package

Absorption

Absorption

Standard Device New Device



UV-LED Applications Map

Disinfection

UVB

UVA

UVC



Irradiance is much improved by array optimization

Key parameters for high power applications:

LED output Power,

Package/Module Thermal management and

Vf uniformity.

Package and

Module design

Improvement

EQ

E(%

), I

rrad

ian

ce (m

W/c

m2)

EQ

E(%

), I

rrad

ian

ce (

mW

/cm

2)



Our Product range allows to address various applications

Components Arrays Modules



UV-LED Market



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

source.

• Recently DUV-LED reached performance allowing to address many

applications.

• Foreseeable technology developments will provide higher efficiencies

and further lifetime improvement.

Conclusion

Source: Aquisense Technology, July 2015

50 mW SMD to be mass-produced this year



Thank you for your attention

Improving Deep UV LED Performance - SEMIsemi.org.cn/semiconchina/mail/160331/1/02-SEMICON... ·...

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