procieee10 high brightness vertical leds on metal alloy

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High Brightness GaN VerticalLight-Emitting Diodes onMetal Alloy for GeneralLighting ApplicationFlexible chip size, capability for high driving-current and excellent heat dissipation,

high-performance device mounting and packaging technology can meet the

requirements of this application.

By Chen-Fu Chu, Chao-Chen Cheng, Wen-Huan Liu, Jiunn-Yi Chu, Feng-Hsu Fan,

Hao-Chun Cheng, Trung Doan, and Chuong Anh Tran

ABSTRACT | In this paper, we show the many advantages of the

GaN-based vertical light-emitting diodes (VLEDs) on metal alloy

over conventional LEDs in terms of: better current spreading,

vertical current path for low operation voltage, better light

extraction, flexible chip size scaling, higher driving current

density, faster heat dissipation, and good reliability. The GaN

VLED on metal alloy exhibits very good current–voltage

behavior with low operated voltage and low serial dynamic

resistance. The low operation junction temperature of GaN

VLED on metal alloy demonstrates excellent heat dissipation

capabilities. Chip size scaling without efficiency loss shows a

unique property of GaN VLED on metal alloy. The GaN VLED on

metal alloy also enables top surface engineering for efficient

light extraction to further light output. A high-power white LED

having efficiency of 120 lumen/W was achieved through a

combination of reflector, surface engineering, and optimiza-

tion of the n-GaN layer thickness. Coupled with good reliability

and mass production ability, the GaN VLED on metal alloy is

very suitable for general lighting application.

KEYWORDS | Driving current density; GaN-based vertical light-

emitting diodes on metal alloy; general lighting application;

heat dissipation; light extraction; operation voltage; power

efficiency; reliability; size scaling

I . INTRODUCTION

GaN-based wide-bandgap semiconductors are widely used

in various applications, such as the mobile phone handset

keypad, LCD backlighting, camera flash, and full-color

outdoor display. Recently, the most popular application

using high-brightness and high-power LEDs is solid-state

general lighting. However, the high-power LED has its

limitation due to technology problems associated with

conventional LEDs on dissimilar base. In order to fabricatehigh-brightness power LEDs for solid-state lighting appli-

cations, there are several serious factors that should be

considered. First, the heat should be managed efficiently.

In general, the efficacy and lifetime drop rapidly as the

junction temperature (Tj) rises. The light output power

efficiency drops by at least 5% as the junction temperature

increases by 20 �C. Secondly, light output power efficiency

of 100 lumens per watt is needed to replace the con-ventional lighting and save energy. Thirdly, chip size

enlargement is inevitable in order to provide enough total

lumens. Fourthly, reliability of 20 000 hours’ lifetime

under continuous operation for the LED in general lighting

is needed to save the maintenance cost. Lastly, the unit

price per chip must be reduced to achieve a reasonable

price for customers.

Manuscript received April 24, 2009; revised November 4, 2009; accepted

November 5, 2009. Date of publication May 3, 2010; date of current version

June 18, 2010.

C.-F. Chu, C.-C. Cheng, W.-H. Liu, J.-Y. Chu, F.-H. Fan, and H.-C. Cheng are with

SemiLEDs Optoelectronics Co., Ltd., Hsinchu, Taiwan (e-mail: [email protected]).

T. Doan and C. A. Tran are with SemiLEDs Corp., Boise, ID 83702 USA.

Digital Object Identifier: 10.1109/JPROC.2009.2037026

Vol. 98, No. 7, July 2010 | Proceedings of the IEEE 11970018-9219/$26.00 �2010 IEEE

II . CONVENTIONAL GaN LED

A. Sapphire SubstrateSemiconductors GaN, AlN, and InN have been grown

primarily on sapphire, most commonly the (0001) ori-

entation but also on the a- and r- planes [1]. In addition, group

III–V nitrides have been grown on SiC, Si, and GaAs. In the

early 1990s, many researchers explored the growth of GaN on

GaAs bases to obtain the metastable zincblende phase of GaN[2]–[4]. Other bases, which were used in order to achieve the

zincblende GaN phase, include Si [5], [6] and SiC [7], [8].

With the exception of SiC, the interest in using these bases

has slowly decreased. The primary reason for the decline in

interest in the zincblende bases is the inherent difficulty in

growing high-quality GaN in the cubic phase. In addition,

the high growth temperature involved precludes the use

of materials with low decomposition temperatures, such asGaAs. Due to the reactivity of nitrogen with Si, amorphous

Si3N4 layers typically form before the GaN deposition,

preventing high-quality GaN films on Si [9], [10] bases.

Therefore, the SiC materials system is challenging the

GaN/sapphire system for dominance in both the opto-

electronic and electronic arena [11]. SiC offers a higher

electrical and thermal conductivity compared to sapphire

and is available in the hexagonal crystal structure. Despitethese advantages, SiC suffers from being substantially more

expensive compared to sapphire and Si. The prohibitive

cost of using SiC has limited its usefulness and availability

to only a small number of groups.

Other suitable base materials have only recently become

commercially available. Almost all the group III–V nitride

semiconductors have been grown on sapphire, despite its

poor structural and thermal match to the nitrides. The pre-ference for sapphire substrates can be ascribed to its wide

availability, hexagonal symmetry, low cost, 8-in-diameter

crystals of good quality,1 transparent nature, and its ease of

handling and pregrowth cleaning. Sapphire is also suitable at

high temperatures ð�1000 �CÞ required for epitaxial growth

using the various chemical vapor deposition (CVD) tech-

niques commonly employed for GaN growth.

However, due to the nonconductivity (electrical resis-tivity ¼ 1011 � 1016 �-cm) and low thermal conductivity

(35 W/m-K) of sapphire substrates, the device process steps

are relatively complicated compared to other compound

semiconductor devices. For devices processed on sapphire

substrates, all contacts must be made from the topside. This

configuration complicates contact and packaging schemes,

resulting in a spreading-resistance penalty and increased

operating voltages [12]. The heat dissipation of sapphiresubstrate was poor; therefore the conventional GaN blue

LEDs on sapphire was typically operated under low current

operation conditions. Therefore, GaN optoelectronics de-

vices fabricated on electrically and high thermally conduct-

ing bases are most desirable. Fig. 1 shows the thermal

conductivity of different bases used today; the vertical LED

on metal alloy has better thermal conductivity than any other

bases such as sapphire, Si, Ge, SiC, and GaN. The betterthermal conductivity suggests heat can be dissipated faster.

B. Configuration of ConventionalGaN LED on Sapphire

1) P-Side Up Configuration: Fig. 2 shows structure

diagrams of the conventional GaN LEDs on sapphire. For

the conventional GaN LEDs on sapphire, the p- and n-

electrode pads are located on the same side as the sapphire,

an insulator. Thus, the total emission area of conventional

GaN LEDs on sapphire is reduced due to the removal ofp-GaN and active layer to expose the n-GaN for n-pad.

2) Current Spreading and Current Path: Fig. 3 shows the

current path of conventional LEDs on sapphire. The current

spreading in conventional LEDs on sapphire from anode to

cathode is laterally along the n-GaN layer. Therefore,

current crowding effects may occur underneath the n-pad,

resulting in higher serial dynamic resistance and higheroperation voltage. Another known issue of the conventional

GaN LEDs on sapphire is the lack of current spreading on

the p-GaN layer due to low conductivity of p-type GaN.

1http://compoundsemiconductor.net/blog/2008/09.

Fig. 1. The thermal conductivity of different base used today.

Fig. 2. The structure diagrams of the conventional GaN LEDs on

sapphire.

Chu et al. : High Brightness GaN Vertical Light-Emitting Diodes

1198 Proceedings of the IEEE | Vol. 98, No. 7, July 2010

Therefore, a semitransparent contact layer (STCL) [13] or

interdigitated designs of electrode [14] on p-GaN for the

conventional GaN LEDs were necessary to spread thecurrent and increase the light output efficiency. Commer-

cially, the specific contact resistance between the STCL and

p-type GaN was typically only about 10�2–10�4 �� cm2.

3) Light Extraction: Due to the absorption of the STCL

[15], the light output power of these conventional LEDs on

sapphire was reduced. To increase the light extraction

efficiency of the conventional LED on sapphire, truncatedhexagonal pyramids or pits were formed on the p-GaN

surface using various techniques such as epitaxy growth [16],

dry etching [17], or wet etching [18]. The drawbacks of the

conventional structure for an effective light extraction lay in

the thickness of the p-GaN layer, which must be thin enough

to avoid reabsorption of photons. In other words, any

engineering of p-GaN surface may affect the active layer

underneath leading to compromised device characteristics.Therefore, the surface engineering on the top of thin p-GaN

(1000–5000 �A) does not leave enough room to engineer.

The second drawback of conventional LEDs on sapphire is

that it lacks a mirror on the backside to reflect photons back

to the rough surface for a better light extraction.

4) Chip Size Scaling: Fig. 4(a) shows the scheme of the

physical geometry emission light direction of the conven-tional LED on sapphire. The GaN/sapphire interface is

transparent. The light generated form the active layer isradiation. Part of the light escapes through the p-GaN to the

air, and the remaining part is discharge from GaN through

the sapphire. The lights were then transmitted from the

four sides and the bottom of the sapphire. Commercially,

the escaped light would then collected by packaging.

However, it is hard to have the surface engineering on the

surface of sapphire due to its chemically stable properties.

Much light could be trapped inside the sapphire because ofthe total internal reflection effect between the sapphire and

air. Once the chip size is enlarged as shown in Fig. 4(b), the

light could be trapped more easily inside the sapphire than

the small chip size. Therefore, the conventional LED on

sapphire has its limitation in chip size scaling. For general

lighting application, the chip size must be scaled up to

obtain enough light for lighting.

5) Heat Analysis: As discussed above, it is tough to form a

good ohmic contact between STCL and p-GaN, and the

current crowding effect that may occur on the bottom of

the n-pad. The majority of heat could be generated and

accumulated from the STCL/p-GaN interface, active layers,

and current crowding area; this generated heat needs to be

dissipated through�5 �m n-GaN layer and�100 �m thick

sapphire. Sapphire’s thickness and its poor thermalconductivity (35 W/mK) make it difficult to dissipate the

generated heat. As a result, the conventional GaN LEDs on

sapphire typically are operated under low current density

conditions in order to prevent thermal problems. The

application of conventional GaN LEDs on sapphire is limi-

ted, especially for the high power LEDs used for solid state

lighting applications.

III . CONFIGURATION OF FLIPCHIP GaN LED

For the flip chip LED, as shown in Fig. 5, the removal of

p-GaN and active layer to expose the n-GaN for n-pad isnecessary, thus the emitting area was reduced. Similarly,

the current transport in flip chip LED from anode to

cathode is lateral along the n-GaN layer. The current

crowding effect generates higher serial dynamic resistance.

Fig. 3. The current path structure diagram of the conventional LEDs

on sapphire.

Fig. 4. (a) The scheme of the physical geometry emission light

direction of the conventional LED on sapphire. (b) The light could be

confined inside the sapphire more than small chip size. Fig. 5. The scheme of flip chip LED structure.


Vol. 98, No. 7, July 2010 | Proceedings of the IEEE 1199

Furthermore, the heat dissipation is comparatively worsethan the vertical structure on metal due to higher thermal

resistance of the solder to the sub-mount. In addition, the

top surface of LED flip chip is sapphire which is very hard to

be engineered for better light extraction through patterning

or texturing. In addition, the combination of thin-film LED

concept with flip-chip technology is reported [19] to

provide surface brightness and flux output advantages over

conventional flip-chip with sapphire on top as Fig. 5configuration. However, the same side p- and n- electrode

has the similar lateral current transportation; it could

generate the high serial dynamic resistance under high

current density operation.

IV. CONFIGURATION OF VERTICALGaN LED ON METAL

1) N-Side Up Configuration: Fig. 6 shows the structure

scheme of the GaN vertical LED on metal. For the GaN

vertical LED on metal, the single n- electrode pad was directly

made on the top of n-GaN. The active layer remained intact

and could emit more light in comparison to the conventionalGaN LEDs on sapphire with the same chip size [20].

2) Current Spreading and Path: The direction of current

path of the GaN vertical LED is vertically from the bottom

anode to the top cathode. Therefore, the vertical current

path [21] without current crowding effect has much lower

serial dynamic resistance than that of the lateral current

path. In addition, the n-GaN has much higher conductivitythan that of p-GaN. The n-GaN can spread the current well

without using any semitransparent conductive layer. Thus,

no light was absorbed by the semitransparent layer, and

higher light output efficiency could be obtained [19], [21].

The better current spreading of n-GaN can help scale up

the chip size without efficiency loss.

3) Light Extraction: To increase the light extraction, GaNVLED on metal was designed to boost the external quantum

efficiency while relieving the demand for a thin p-GaN layer.

To form the hexagonal pyramids on top of n-GaN, chemical

etching or photoenhance chemical etching were reported

[22]. All the surface engineering occurs on the thick, over4 �m, n-GaN layer. The top surface is roughened,

allowing more photons to escape from the surface.

The reflectivity of metal/GaN interface also plays an

important role to enhance the light extrication. The ref-

lectivity from the interface of metal/GaN interface can be

estimated by using the well-known formula 1-1 [23], [24]

for reflection of a wave perpendicularly incident from

media 1 onto the plane boundary of a solid with refractiveindex n. The ratio R of reflected-to-incident irradiance is

given by the Fresnel expression

R ¼ ðns � nmÞ2 þ k2m

ðns þ nmÞ2 þ k2m

(1-1)

where ns is the refractive index of semiconductor, nm is

the refractive index of metal, and km is extinction coef-

ficient of metal. Table 1 [25]–[28] gives the parameters

for different materials and GaN material at the wave-

length of 400, 460 nm. The calculated reflectivity (R) ofFig. 6. The structure diagrams of the GaN vertical LED on metal.

Table 1 The Parameters for Different Metals and GaN Material at the

Wavelength of 400, 460 nm. [25]–[28]



GaN/material interface was also listed in Table 1. For

the blue GaN LEDs, the emission wavelength is at about

460 nm. Fig. 7 shows the reflectivity of different metalsversus wavelength measured by depositing the metals on

sapphire. Both silver and aluminum show the higher

reflectivity for the standard blue emission range. To form

the high-reflectivity metal or its alloy as the reflector, more

light output power can be obtained.

4) Chip Size Scaling: Fig. 8(a) shows the scheme of the

physical geometry emission light direction of the GaN VLEDon metal. The GaN VLED on metal has a high reflectivity

metal as a mirror to reflect the light. Because the thickness of

GaN LED epitaxy layer structure is only about 4–6 �m, the

light from the active layer is directly reflected by the bottom

reflector. Almost all of the light is vertically emitted through

the top surface. Once the chip size is enlarged, as shown in

Fig. 8(b), the light emission behaves similarly as the small

chip size. Almost all of the light is emitted vertically throughthe top surface. Therefore, there is no limitation of GaN

VLED on metal in chip size scaling. For the general lighting

application, the emission area should be large enough to

provide enough lumens. The GaN VLED structure is a

suitable solution to achieve the requirement.

5) Heat Analysis: Fig. 9 shows the current path scheme of

the GaN VLED on metal. For GaN VLED on metal, the heat

could be generated from the active layers and the metal

contact to p-type GaN interface. Nevertheless, the thin p-type

GaN ð�0.2 �mÞ directly laid on the layers of high thermal

conductivity metal alloy material (400 W/mK) can dissipate

the heat more quickly. The current path in the GaN VLEDsstructure flows vertically from the bottom anode to the top

cathode. Therefore, the vertical current path without current

crowding effect has much lower serial dynamic resistance

than that of the lateral current path. Consequentially, faster

heat dissipation and higher current operation can be achieved.

The structure with GaN VLED on metal is most suitable for

high-power solid-state lighting application.

V. HIGH-BRIGHTNESS GaN VERTICALLIGHT-EMITTING DIODE ONMETAL ALLOY

A. StructureA schematic cross-section image of VLED on metal

alloy is shown in Fig. 10. The LED structure consists of a

mirror, directly deposited on metal alloy and acting as

anode and reflector, the 0.2-�m-thick p-GaN/p-AlGaN

layer, an InGaN/GaN multiple quantum wells active layer,and a 4-�m-thick n-GaN layer. Then to enhance the light

extraction, the n-GaN surface is patterned. In this

configuration, the current can pass from anode to cathode

vertically, avoiding the current crowding effect observed

with conventional GaN LED on sapphire. The photons

generated in the active layer can escape without passing

through any semitransparent conductive contact layer.

Meanwhile, the photons can be reflected by the mirror atvisible wavelength range to avoid the geometry limited

effect observed from the conventional configuration of

large GaN LEDs on sapphire.

B. Results and DiscussionFig. 11 shows the current–voltage (I–V) characteristics

for the GaN VLED on metal alloy and the conventional LEDs

Fig. 7. The reflectivity of different metals versus wavelength

measured by depositing the metals on sapphire.

Fig. 8. The scheme of the physical geometry emission light direction

of the GaN VLED on metal for (a) small chip size and

(b) large chip size is enlarged.

Fig. 9. The current path scheme of the GaN VLED on metal.



on sapphire. The operation voltage at 350 mA is about 3.4 V

for the conventional LEDs on sapphire and 3.0 V for the GaN

VLED on metal alloy. From the slope of I–V curve, theaverage dynamic series resistances of these two different

device configurations are 1.1 � for the conventional LEDs on

sapphire and 0.7 � for the GaN VLED on metal alloy. The

higher average dynamic serial resistance of the conventional

LEDs on sapphire could be due to the lateral current path

and the current crowded effect on the bottom of n-pad. The

lower operation voltage and average dynamic series

resistance of the GaN VLED on metal alloy has better lightoutput efficiency and operation performance compared with

the conventional GaN LEDs on sapphire.

Fig. 12 shows the comparison of the light output power–

current (L–I) characteristics for the GaN VLED on metal

alloy and the conventional LEDs on sapphire. The light

output power of the conventional LEDs on sapphire peaked

around 1000 mA and then declined quickly after 1000 mA.

Poor heat dissipation capability was reasoned for thedegradation. On the contrary, the light output power of

the GaN VLED on metal alloy can sustain higher current of

3000 mA or higher without light output power saturation.

The high current operation behavior showed the superior

heat dissipation of the metal alloyed and allowed higher

current injection to obtain higher light output power, which

is especially needed for the general lighting application.

A conventional LED on sapphire and the GaN VLED onmetal alloy of the same size of 40 mil were mounted onto

lead-frames using silver epoxy, and the junction temper-

ature was measured as a function of current. Fig. 13 shows

the junction temperature as a function of current for the

two types of LED structure. The GaN VLED on metal alloy

Fig. 10. A schematic cross-section image of VLEDs on metal alloy.

Fig. 11. The I–V characteristics of a 40 mil chip for the GaN VLED

on metal alloy and the conventional LEDs on sapphire.

Fig. 12. The comparison of the light output L–I characteristics of a

40 mil chip for the GaN VLED on-metal alloy and the conventional

LEDs on sapphire.



has an estimated lower thermal resistance of 74.2 K/W

than the 89.1 K/W of conventional LED on sapphire.

A striking difference between the GaN VLED onmetal alloy and the conventional LEDs on sapphire is the

scaling effect shown in Fig. 14. The normalized

extraction efficiency of the GaN VLED on metal alloy

is not sensitive to the chip size, while the conventional

LEDs on sapphire exhibit a significant drop in efficiency

for larger chips. For lighting application, the chip size

must be large in order to generate enough brightness

required for this application.We use the same technology platform with different

n-electrode patterns design to scale up and down all sizes.

The design rule is taking the n-GaN current spreading into

account. Each one n-electrode designed line can spread the

current to be about 150� 200 �m. Therefore, bigger chip

size needs additional n-electrode line to help for better

current spreading. Fig. 15 shows the blue emission pictures

and the n-electrode design patterns for different chip size

ranging from 15 to 80 mil. The GaN VLED on metal alloy

fabrication technology can apply to all chip sizes withoutefficiency drop.

Fig. 16 shows structural diagrams of the conventional

GaN LED on sapphire. For the conventional GaN LED on

sapphire, the p-GaN layer thickness is usually kept below

2000 �A, as p-GaN absorbs photons in the wavelength of the

interested spectrum. To increase the light extraction effi-

ciency, either truncated hexagonal pyramids or pits were

formed on the p-GaN surface using various techniques. Thedrawbacks of the conventional structure for an effective light

extraction lay in the thickness of p-GaN layer, which must be

thin enough to avoid reabsorption of photons. In other

words, any engineering of p-GaN surface may affect the

active layer underneath, leading to compromised device

characteristics. The second drawback of conventional LEDs

on sapphire is that it lacks a mirror on the backside to reflect

photons back to the rough surface for better light extraction.To overcome these shortcomings, the GaN VLED on

metal alloy was designed to boost the external quantum

efficiency while relieving the demand for a thin p-GaN

Fig. 13. The junction temperature as a function of current for the

two types of LED structure.

Fig. 14. The scaling effect for the GaN VLED on metal alloy and the

conventional LEDs on sapphire. The efficiency was normalized to a

chip size of 350 �m.

Fig. 15. The emission pictures for different chip size ranging from

15 to 80 mil.

Fig. 16. The structural diagrams of the conventional GaN LED

on sapphire.



layer. Fig. 17(a) and (b) shows the first and second ver-

sions of the GaN VLED on metal alloy. All the surface

engineering occurs on the thick n-layer (> 4 �m). In the

first version of the GaN VLED on metal alloy, the GaN LED

structure is placed on a high-reflectivity surface, as shown

in Fig. 17(a), with the top surface roughened by etching to

allow more photons to escape the surface. To further

enhance the number of photons extracted from the surface,a new technique to form a corrugated pyramid shaped

(CPS) surface, as shown in Fig. 17(b), was developed. The

new CPS surface increases the surface areas having angular

randomization, allowing more scattering of photons.

Fig. 18 shows the scanning electron microscope (SEM)

surface of the GaN VLED on metal alloy of version 1. Fig. 19

Fig. 17. The (a) first and (b) second versions of the GaN VLED

on metal alloy.

Fig. 18. The (a) top view and (b) side view of the SEM surface for

the GaN VLED on metal alloy of first version.

Fig. 19. The (a) top view and (b) side view of the SEM surface for the

GaN VLED on metal alloy of second version with CPS structure.

Fig. 20. Comparison of the light output L–I characteristics for the GaN

VLED on metal alloy of first version, and second version with CPS

structure.

Fig. 21. The far-field emission pattern for the first version

and second version.

Fig. 22. The brightness distribution of the GaN VLED on metal alloy

with different N-GaN thicknesses.



shows the top view and side view of the SEM surface for the

GaN VLED on metal alloy of version 2 with CPS structure.

At 350 mA, an improvement of 20% is observed for the GaN

VLED on metal alloy with CPS surface, as shown in Fig. 20.

Fig. 21 shows the far-field emission pattern for the first

version and the second version. The uniform and good

Lambertian light patterns can be obtained by the vertical

LED structure. The GaN VLED on metal alloy with CPS topsurface had higher total light out power intensity. The light

pattern of the GaN VLED on metal alloy with CPS surface

also showed a higher ratio of light output power in the

power angle from 30� to 150� compared to the first version

GaN VLEDs.

Another aspect of the GaN VLED on metal alloy is that

the n-GaN layer averaged thickness can be tailored to be

thinner. Any reabsorption of photons in the n-layer by freeelectrons or by the mid-gap states will lead to a loss of

efficiency. Besides providing higher extraction (more

scattering sites), the GaN VLED on metal alloy with CPS

technology also lowers the effective n-GaN thickness,

minimizing the reabsorption effects without sacrificing the

quality of the active layers. Fig. 22 shows the brightness

distribution of the GaN VLED on metal alloy with different

n-GaN thicknesses. A reduction of n-GaN layer thickness

from 6 to 4.5 �m improves 12% of brightness.

C. ReliabilityFor a reliability study, we selected 1 mm2 GaN VLED

on metal alloy chips with a light output power equivalent

to converted white light of over 120 lumens/W (Table 2).

The chips then were packaged using silicone as filling.

The packaged chips were mounted on a heat sink, and

measurements were carried out in a close space with stable

ambient temperature. A life test was performed on the

GaN VLED on metal alloy at a forward current of 350 mA

at ambient room temperature. As shown in Fig. 23, thedrop of light output power is quite little and can be kept

below 10% even after the burn-in test of 5000 h. In case of

daily life application at the ambient room temperature, no

Table 2 The 40 mil Chip Packaged With Phosphor to Produce White Light.

(IS System, ISP-150, Keithley 2430 at 350 mA)

Fig. 23. The drop of light output power after the burn-in test of 5000 h.

Fig. 24. The stability of light output power after 1000 times

thermal shock.

Fig. 25. The stability of operation voltage at 350 mA after 1000

cycles thermal shock.



degradation of light output has been observed so far as

referred to the BRT[ points.The thermal shock aging for the packed VLED chips

is measured ranging from the temperature of �40 �C(15 min) to 125 �C (15 min). After 1000 times high and low

recycle temperature aging, the packaged VLED chips show

no degradation of the light output power (Fig. 24) and no

fail of the operation voltage at 350 mA (Fig. 25).

In some special solid-state lighting application, such as

lighting equipment in the desert or outside of an airplane,the packaged VLED chips can be sustained in harsher

environments. Fig. 26 shows the reflow testing tempera-

ture profile. Fig. 27 shows the packaged VLED chips have

no light output degradation and no operation voltage

failures after ten times reflow cycle testing.

VI. CONCLUSION

In conclusion, the GaN VLED on metal alloy was presented

and characterized. Very low dynamic resistance, low

operation voltage, excellent heat dissipation, and good

reliability of the GaN VLED on metal alloy were proven.An efficiency of 120 lumens/W or better was achieved,

rendering the GaN VLED on metal alloy very suitable for

general lighting application. h

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Fig. 26. The reflow testing temperature profile.Fig. 27. The reliability of packaged VLED chips after ten times reflow.



ABOUT T HE AUTHO RS

Chen-Fu Chu received the B.S. degree in electrical

engineering from Tamkang University, Taiwan,

in 1995, the M.S. degree in optical sciences from

National Central University, Taiwan, in 1998, and

the Ph.D. degree in Electro-Optical Engineering

from National Chiao-Tung University, Taiwan,

in 2003.

He is a Research Director with SemiLEDs

Optoelectronics Co., Ltd. In 2003, he joined High-

link Technology Corp. as a Scientist. In 2005, he

joined SemiLEDs Cooperation as a Chief Scientist. He has published more

than 25 scientific and technical journal papers and 50 conference papers.

Chao-Chen Cheng, photograph and biography not available at the time

of publication.

Wen-Huan Liu, photograph and biography not available at the time of

publication.

Jiunn-Yi Chu, photograph and biography not available at the time of

publication.

Feng-Hsu Fan, photograph and biography not available at the time of

publication.

Hao-Chun Cheng, photograph and biography not available at the time of

publication.

Trung Doan, photograph and biography not available at the time of

publication.

Chuong Anh Tran received the B.S. degree in

physics from Czech Technical University, Czech

Republic, in 1987 and the Ph.D. degree from the

University of Montreal, Montreal, PQ, Canada, in

1993.

He is President and COO of SemiLEDs Corp. He

has extensive educational and professional expe-

rience, including nearly 15 years of working

experience, in the field of optoelectronics. He

joined Emcore in 1993 as a Senior Technical Staff

Member and became one of the key members of the team that developed

the first commercial reactor for InGaN LED. In 1999, he joined Gelcore,

then a joint venture between Emcore and GE Lighting, focusing on solid-

state lighting. In 2001, he joined Highlink Technology Corp. as Vice

President. He has published more than 70 technical papers in numerous

scientific journals and has participated as a Guest Speaker at numerous

conferences, including SPIE, Photonics West, MRS meetings, European

MRS, and International MOVPE conferences.

Dr. Tran received the Quebec Government FCAR Excellence

Scholarship.



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