IEEE TRANSACTIONS ON ADVANCED PACKAGING, VOL. 28, NO. 2, MAY 2005 273

Nitride-Based Flip-Chip ITO LEDsS. J. Chang, C. S. Chang, Y. K. Su, Senior Member, IEEE, C. T. Lee, Senior Member, IEEE, W. S. Chen, C. F. Shen,

Y. P. Hsu, S. C. Shei, and H. M. Lo

Abstract—Nitride-based flip-chip indium–tin–oxide (ITO) light-emitting diodes (LEDs) were successfully fabricated. It was foundthat the forward voltage and the 20 mA output power of the flip-chip ITO LED were 3.32 V and 14.5 mW, respectively. Although theoperation voltage of such a flip-chip ITO LED was slightly larger,it was found that its output power was much larger than those ofconventional nonflip-chip LEDs. It was also found that flip-chipITO LEDs were more reliable.

Index Terms—Flip-chip, GaN, indium–tin–oxide (ITO), light-emitting diode (LED).

I. INTRODUCTION

RECENTLY, tremendous progress has been achieved in ni-tride-based materials [1]–[6]. With a wide direct bandgap

energy, these nitride-based materials are currently among themost promising and important materials in the optoelectronicindustry. At room temperature, the bandgap energy of AlInGaNvaries from 0.8 to 6.2 eV depending on its composition. There-fore, III–V nitride semiconductors are particularly useful forlight emitting diodes (LEDs) in the short wavelength region[7]–[13]. This has resulted in a variety of applications, suchas traffic lights, full color displays, and solid-state lighting. Inthe case of lighting, white light LEDs are already commerciallyavailable by combining a phosphor wavelength converter with aGaN blue LED chip. The blue light emitted from the GaN LEDchip is absorbed by the phosphor and re-emitted as long-wave-length phosphorescence. Thus, white light can be generated bythe combination of the two emission bands. Although lifetimeof white LEDs is much longer than those of light bulbs andfluorescent lamps, output power of the current white LEDs isstill low. In other words, we need to improve the output in-tensity of nitride-based blue LED chips before we can realizefeasible nitride-based white LED lamps. Conventional nitride-based blue LEDs use semi-transparent Ni/Au on p-GaN as theupper contacts. However, the transmittance of Ni/Au is onlyaround 55–75%. One possible way to enhance output intensityis to use the transparent indium–tin–oxide (ITO) as the uppercontact layers of nitride-based LEDs [14]–[17]. Recently, wehave demonstrated blue LEDs with n -InGaN/GaN short pe-riod superlattice (SPS) tunneling contact layers and ITO uppercontacts [18], [19]. Compared with conventional nitride-based

Manuscript received January 22, 2004; revised September 7, 2004. This workwas supported by the National Science Council under Research Grants NSC90-2215-E-008-043 and NSC 90-2112-M-008-046.

S. J. Chang, C. S. Chang, Y. K. Su, C.-T. Lee, W. S. Chen, C. F. Shen, andY. P. Hsu are with the Institute of Microelectronics and Department of ElectricalEngineering, National Cheng Kung University, Tainan, 70101, Taiwan, R.O.C.

S. C. Shei and H. M. Lo are with the South Epitaxy Corporation, Hsin-Shi744, Taiwan, R.O.C.

Digital Object Identifier 10.1109/TADVP.2005.846941

Fig. 1. Schematic diagrams of (a) conventional nitride-based LEDs and(b) flip-chip LEDs.

blue LEDs with Ni/Au upper contacts, it was found that wecould achieve a much larger electroluminescence (EL) inten-sity by using ITO upper contacts due to the transparent natureof ITO. However, a significant amount of photons emitted fromthe ITO upper contact layers are still obscured by the bondingpads of the devices, as shown in Fig. 1(a). As a result, externalquantum efficiency and output power of the packaged LEDs willboth become smaller. One possible way to solve this problemis to use flip-chip technology [20]–[25], as shown in Fig. 1(b).By using flip-chip technology, we should be able to achieve alarger output power since no bonding pads or wires exist on topof the devices so that photons could be emitted freely from thesubstrates. Also, we should be able to further improve the outputpower by depositing a reflector layer at the bottom of the devicesso that down-emitting photons could be reflected upward. In thispaper, we applied such flip-chip technology to nitride-based ITOLEDs with Al reflector layers. The physical, electrical, and op-tical properties of the fabricated devices will be reported. Com-parisons between flip-chip ITO LEDs, nonflip-chip ITO LEDs,and nonflip-chip Ni/Au LEDs will also be made.

II. EXPERIMENTS

The InGaN/GaN epitaxial layers used in this investigationwere all grown by metalorganic chemical vapor deposition(MOCVD) on c-face 2-in sapphire Al O (0001) substrates.The LED structure consists of a 50-nm-thick GaN nucleationlayer grown at 550 C, a 3- m-thick Si-doped n-GaN bufferlayer grown at 1050 C, an unintentionally doped InGaN/GaNmultiquantum well (MQW) active region grown at 770 C, a50-nm-thick Mg-doped p Al Ga N electron-blocking

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274 IEEE TRANSACTIONS ON ADVANCED PACKAGING, VOL. 28, NO. 2, MAY 2005

layer grown at 1050 C, a 0.25- m-thick Mg-doped p-GaNlayer grown at 1050 C, and an InGaN/GaN n -SPS tunnelcontact structure. The InGaN/GaN MQW active region con-sists of five pairs of 3-nm-thick In Ga N well layersand 7-nm-thick GaN barrier layers. On the other hand, then -SPS tunnel contact structure consists of four pairs ofn In Ga N/GaN (0.5 nm/0.5 nm). By growing suchSPS structures on top of the p-GaN cap layer, one couldachieve a good “ohmic” contact through tunneling when then InGaN/GaN p GaN junction was properly reversebiased [18], [19]. The as-grown samples were subsequentlyannealed at 750 C in N for 20 min to active Mg in the p-typelayers. Surfaces of the samples were then partially etched untilthe n-type GaN layers were exposed. An 80-nm-thick ITO layerand a 200-nm-thick Al reflective mirror were subsequentlyevaporated onto the sample surfaces (i.e., Si-doped n -SPS).Since ITO is electrically conductive with a high transparencyand Al is highly reflective, we should be able to achievemuch larger light outputs by the reflective ohmic contacts inthe flip-chip design. In order to measure the reflectance of themirror, we also deposited the same ITO and Al layers onto glasssubstrates. The reflection spectra of the deposited ITO/Al filmswere then measured by a Hitachi U3010 spectrophotometer. Onthe other hand, Ti/Al/Ti/Au contacts were deposited onto theexposed n-type GaN layers to serve as the n-type electrodes.SiO layers were then deposited over all wafers by plasma-en-hanced chemical vapor deposition (PECVD. During SiOdeposition, we introduced 60 sccm SiH and 20 sccm N O intothe PECVD chamber, while the deposition temperature and theprocess pressure were kept at 250 C and 10 mTorr, respec-tively. Photolithography and hydroflouric acid (HF) solutionetching were subsequently performed to define the P/N padpatterns for the bump electroplating. It should be noted that stepcoverage of the SiO films should be well controlled to coverthe entire chips. Prior to electroplating, we first sputtered TiWonto the wafers to serve as the under bump material (UBM).Sn/Au 15 m 5 m layers were then electroplated on thesamples while P/N bumps were defined by the lift-off process.The processed wafers were subsequently lapped down to about120- m thick. We then used scribe and break to fabricate the320 400 m flip-chip ITO chips. During the bonding process,the chips were picked, orientated, and flipped by a die bondersystem. A scanning electron microscope (SEM) was then usedto physically characterize the fabricated flip-chip samples. Forcomparison, nonflip-chip ITO and nonflip-chip Ni/Au LEDswere also fabricated with exactly the same epitaxial structureand the same chip size. These chips were then encapsulatedwith epoxy and packaged into LED lamps. It should be notedthat flip-chip LEDs were soldered onto Si submounts prior topackaging. Current–voltage (I–V) measurements of the fabri-cated LED lamps were then performed at room temperature(RT) by an HP4156 semiconductor parameter analyzer. RTelectroluminescence (EL) characteristics of these lamps werealso evaluated by injecting different amount of dc currents intothese LEDs. The output powers were then measured using themolded LEDs with an integrated sphere detector from top ofthe devices. Reliability tests of these LED lamps were alsoperformed.

Fig. 2. (a) Cross-sectional SEM pictures of the devices prior to electroplatingand (b) an SEM picture of the entire chip after electroplating and liftoff.

III. RESULTS AND DISCUSSIONS

From the normalized reflection spectrum of the ITO/Al layers(not shown here), it was found that the deposited ITO/Al layerswere indeed highly reflective with a reflectance larger than 85%when the incident light wavelength was shorter than 690 nm. Inthe wavelength region between 400 and 495 nm, we could evenachieve a reflectance larger than 90%. Thus, we should be able toeffectively reflect the down-emitting photons upward by usingITO/Al as the reflector in the flip-chip scheme shown in Fig. 1(b).Fig. 2(a) shows cross-sectional SEM pictures of the devicesprior to electroplating. It can be seen clearly that step coverageof the PEVCD SiO films was good. Such good step coveragecould prevent an unexpected short circuit, which might occurafter package. Fig. 2(b) shows an SEM picture of the entire chipafter electroplating and liftoff. As shown in this figure, the twoSn/Au bumps were well defined after liftoff. These well-definedbumps are important for the subsequent flip-chip process.

Fig. 3 shows measured intensity–current-voltage (L–I–V)characteristics of the flip-chip ITO LEDs. For comparison,L–I–V characteristics of the nonflip-chip ITO and nonflip-chipNi/Au LEDs were also shown in the same figure. From the I–Vcurves, we found that the 20-mA forward voltages measuredfrom the flip-chip ITO, nonflip-chip ITO, and nonflip-chipNi/Au LEDs were 3.32, 3.24, and 3.03 V, respectively. In otherwords, we achieved the lowest 20-mA operation voltage fromthe conventional nonflip-chip Ni/Au LED. The 0.21-V largeroperation voltage observed from the nonflip-chip ITO LEDcould be attributed to the larger contact resistance between ITOand the underneath n -SPS structure [14], [15]. Since the 600nm-thick PECVD SiO passivation layer was grown at 250 C,

CHANG et al.: NITRIDE-BASED FLIP-CHIP ITO LEDs 275

Fig. 3. Measured L–I–V characteristics of the three different kinds of LEDs.

slight interfacial mixing might have occurred in the n -SPSstructure. We believe such interfacial mixing could result in alarger specific contact resistance and, thus, an increase in theLED operation voltage. Although the specific contact resis-tance of the flip-chip ITO LED was the largest among the threesamples, the 3.32-V forward voltage was still reasonably good.

The intensity–current (L–I) characteristics of these three dif-ferent kinds of LEDs were also shown in the same figure. It wasfound that output power of the nonflip-chip ITO LED was largerthan that of the nonflip-chip Ni/Au LED. This is due to the factthat ITO is more transparent than Ni/Au. It was also found thatoutput power of the flip-chip ITO LED was larger than that ofthe nonflip-chip ITO LED. This can again be attributed to thefact that no bonding pads or wires exist on top of the flip-chipITO LED. It should also be noted that the refractive indexes ofsapphire substrate and GaN are 1.7 and 2.5, respectively. Thus,photons generated in the LEDs should be able to find the es-cape cone easier from the sapphire/air interface (i.e., flip-chipLEDs), as compared to the GaN/air interface (i.e., nonflip-chipLEDs). In other words, the smaller refractive index of sapphiresubstrate could also enhance the LED output intensity. With a20-mA current injection, it was found that output powers wereonly 9.1 and 5.6 mW for the nonflip-chip ITO LED and the non-flip-chip Ni/Au LED, respectively. In contrast, output power offlip-chip ITO LED could reach 14.5 mW with the same currentinjection. Fig. 4 shows life tests of relative luminous intensitymeasured from these three LEDs, normalized to their respectiveinitial readings. During life test, all three LEDs were driven by a30-mA current injection at RT. After 1000 h stress, it was foundthat the luminous intensity only decreased by 9% for the flip-chip ITO LED. In contrast, the luminous intensity decreased by29% and 20% for the nonflip-chip ITO LED and the nonflip-chipNi/Au LED, respectively, during the same period. It is known thatmost of the heat was generated in the MQW active region. Asshown in Figs. 1(a) and 1(b), the thermal path between the MQWactive region and the heat sink is much shorter for the flip-chipLEDs. Thus, flip-chip technology can be used to improve LEDs’thermal properties. As a result, most heat generated in the MQWactive region could flow easily to the Si submount for the flip-chipLED. With less thermal effect, we, thus, achieved a longer life-time from the flip-chip ITO LED, as shown in Fig. 4.

Fig. 4. Life tests of relative luminous intensities measured from the LEDlamps, normalized to their respective initial readings.

IV. SUMMARY

In summary, the fabrication of nitride-based flip-chip ITOLEDs has been successfully demonstrated. Although the op-eration voltage of such flip-chip ITO LED was slightly larger,it was found that its output power was much larger thanthose of conventional nonflip-chip LEDs. It was also foundthat flip-chip ITO LED was more reliable due to the shorterthermal path.

REFERENCES

[1] S. Nakamura, T. Mukai, and M. Senoh, “Candela-class high brightnessInGaN/AlGaN double-heterostructure blue light-emitting diodes,” Appl.Phys. Lett., vol. 64, pp. 1687–1689, 1994.

[2] I. Akasaki and H. Amano, “Crystal growth and conductivity controlof group III-nitride semiconductors and their applications to shortwavelength light emitters,” Jpn. J. Appl. Phys., vol. 36, pp. 5393–5408,1997.

[3] S. J. Chang, W. C. Lai, Y. K. Su, J. F. Chen, C. H. Liu, and U. H. Liaw,“InGaN/GaN multiquantum well blue and green light emitting diodes,”IEEE J. Sel. Topics Quantum Electron., vol. 8, no. 2, pp. 278–283,Mar./Apr. 2002.

[4] S. J. Chang, C. H. Chen, P. C. Chang, Y. K. Su, P. C. Chen, Y. D. Jhou,H. Hung, C. M. Wang, and B. R. Huang, “Nitride-based LEDs withp-InGaN capping layer,” IEEE Trans. Electron Devices, vol. 50, no. 12,pp. 2567–2570, Dec. 2003.

[5] S. J. Chang, M. L. Lee, J. K. Sheu, W. C. Lai, Y. K. Su, C. S. Chang, C. J.Kao, G. C. Chi, and J. M. Tsai, “GaN metal-semiconductor-metal pho-todetectors with low-temperature GaN cap layers and ITO metal con-tacts,” IEEE Electron Device Lett., vol. 24, no. 4, pp. 212–214, Apr.2003.

[6] L. W. Wu, S. J. Chang, Y. K. Su, R. W. Chuang, Y. P. Hsu, C. H. Kuo,W. C. Lai, T. C. Wen, J. M. Tsai, and J. K. Sheu, “In Ga N/GaNMQW LEDs with a low temperature GaN cap layer,” Solid-State Elec-tron., vol. 47, pp. 2027–2030, 2003.

[7] R. Windisch, B. Dutta, M. Kuijk, A. Knobloch, S. Meinlschmidt, S.Schoberth, P. Kiesel, G. Borghs, G. H. Dohler, and P. Heremans, “40%efficient thin film surface textured light emitting diodes by optimizationof natural lithography,” IEEE Trans. Electron Devices, vol. 47, no. 7, pp.1492–1498, Jul. 2000.

[8] Y. C. Lin, S. J. Chang, Y. K. Su, T. Y. Tsai, C. S. Chang, S.C. Shei, S. J. Hsu, C. H. Liu, U. H. Liaw, S. C. Chen, and B.R. Huang, “Nitride-based light-emitting diodes with Ni/ITO p-typeohmic contacts,” IEEE Photon. Technol. Lett., vol. 14, no. 12, pp.1668–1670, Dec. 2002.

276 IEEE TRANSACTIONS ON ADVANCED PACKAGING, VOL. 28, NO. 2, MAY 2005

[9] L. W. Wu, S. J. Chang, Y. K. Su, R. W. Chuang, T. C. Wen, C. H. Kuo,W. C. Lai, C. S. Chang, J. M. Tsai, and J. K. Sheu, “Nitride-basedgreen light emitting diodes with high temperature GaN barrier layers,”IEEE Tran. Electron Devices, vol. 50, no. 8, pp. 1766–1770, Aug.2003.

[10] C. S. Chang, S. J. Chang, Y. K. Su, Y. Z. Chiou, Y. C. Lin, Y.P. Hus, S. C. Shei, J. C. Ke, H. M. Lo, S. C. Chen, and C. H.Liu, “InGaN/GaN light emitting diodes with rapid thermal annealedNi/ITO p-contacts,” Jpn. J. Appl. Phys., pt. 1, vol. 42, no. 6A, pp.3324–3327, 2003.

[11] Y. Z. Chiou, Y. K. Su, S. J. Chang, J. F. Chen, C. S. Chang, S. H. Liu,Y. C. Lin, and C. H. Chen, “Transparent TiN electrodes in GaN metal-semiconductor-metal ultraviolet photodetectors,” Jpn. J. Appl. Phys., pt.1, vol. 41, no. 6A, pp. 3643–3645, Jun. 2002.

[12] S. J. Chang, C. H. Kuo, Y. K. Su, L. W. Wu, J. K. Sheu, T. C.Wen, W. C. Lai, J. F. Chen, and J. M. Tsai, “400 nm InGaN/GaNand InGaN/AlGaN multiquantum well light-emitting diodes,” IEEE J.Sel. Topics Quantum Electron., vol. 8, no. 4, pp. 744–748, Jul./Aug.2002.

[13] J. K. Sheu, J. M. Tsai, S. C. Shei, W. C. Lai, T. C. Wen, C. H. Kou, Y. K.Su, S. J. Chang, and G. C. Chi, “Low-operation voltage of InGaN/GaNlight-emitting diodes with Si-doped In Ga N/GaN short-period su-perlattice tunneling contact layer,” IEEE Electron. Device Lett., vol. 22,no. 10, pp. 460–462, Oct. 2001.

[14] K. M. Chang, J. Y. Chu, and C. C. Cheng, “Highly reliable GaN-basedlight-emitting diodes formed by p � In Ga N � ITO structure,”IEEE Photon. Technol. Lett., vol. 16, no. 8, pp. 1807–1809, Oct.2004.

[15] S. Y. Kim, H. W. Jang, and J. L. Lee, “Effect of an indium-tin-oxideoverlayer on transparent Ni/Au ohmic contact on p-type GaN,” Appl.Phys. Lett., vol. 82, pp. 61–63, 2003.

[16] S. M. Pan, R. C. Tu, Y. M. Fan, R. C. Yeh, and J. T. Hsu, “Enhancedoutput power of InGaN-GaN light-emitting diodes with high-trans-parency nickel-oxide-indium-tin-oxide ohmic contacts,” IEEE Photon.Technol. Lett., vol. 15, no. 5, pp. 646–648, May 2003.

[17] , “Improvement of InGaN-GaN light-emitting diodes with surface-textured indium-tin-oxide transparent ohmic contacts,” IEEE Photon.Technol. Lett., vol. 15, no. 5, pp. 649–651, May 2003.

[18] C. S. Chang, S. J. Chang, Y. K. Su, C. H. Kuo, W. C. Lai, Y. C. Lin,Y. P. Hsu, S. C. Shei, J. M. Tsai, H. M. Lo, J. C. Ke, and J. K. Sheu,“High brightness InGaN green LEDs with an ITO on n++-SPS uppercontact,” IEEE Trans Electron. Dev., vol. 50, no. 11, pp. 2208–2212,Nov. 2003.

[19] S. J. Chang, C. S. Chang, Y. K. Su, R. W. Chuang, Y. C. Lin, S. C. Shei,H. M. Lo, H. Y. Lin, and J. C. Ke, “Highly reliable nitride-based LEDswith SPS+ITO upper contacts,” IEEE J. Quantum Electron., vol. 39, no.11, pp. 1439–1443, Nov. 2003.

[20] J. J. Wierer et al., “High-power AlGaInN flip-chip light-emittingdiodes,” Appl. Phys. Lett., vol. 78, pp. 3379–3381, 2003.

[21] J. Song, D. S. Leem, J. S. Kwak, O. H. Nam, Y. Park, and T. Y. Seong,“Low resistance and reflective Mg-doped indium oxide-Ag ohmic con-tacts for flip-chip light-emitting diodes,” IEEE Photon. Technol. Lett.,vol. 16, no. 6, pp. 1450–1452, Jun. 2004.

[22] A. Chitnis, J. Sun, V. Mandavilli, R. Pachipulusu, S. Wu, M. Gaevski, V.Adivarahan, J. P. Zhang, M. A. Khan, A. Sarua, and M. Kuball, “Self-heating effects at high pump currents in deep ultraviolet light-emittingdiodes at 324 nm,” Appl. Phys. Lett., vol. 81, no. 18, pp. 3491–3493,2002.

[23] M. Koike, N. Shibata, H. Kato, and Y. Takahashi, “Development of highefficiency GaN-based multiquantum-well light-emitting diodes and theirapplications,” IEEE J. Sel. Topics Quantum Electron., vol. 8, no. 2, pp.271–277, Mar./Apr. 2002.

[24] K. Tadatomo, H. Okagawa, Y. Ohuchi, T. Tsunekawa, T. Jyouichi, Y.Imada, M. Kato, H. Kudo, and T. Taguchi, “High output power InGaNultraviolet light plus emitting diodes fabricated on patterned substratesusing metalorganic vapor phase epitaxy,” Phys. Stat. Sol. (A), AppliedResearch, vol. 188, no. 1, pp. 121–125, 2001.

[25] K. Tadatomo, H. Okagawa, Y. Ohuchi, T. Tsunekawa, Y. Imada, M.Kato, and T. Taguchi, “High output power InGaN ultraviolet light-emit-ting diodes fabricated on patterned substrates using metalorganic vaporphase epitaxy,” Jpn. J. Appl. Phys., pt. 2, vol. 40, no. 6B, pp. 583–585,2001.

S. J. Chang was born in Taipei, Taiwan, R.O.C., onJanuary 17, 1961. He received the B.S.E.E. degreefrom the National Cheng Kung University (NCKU),Tainan, Taiwan, in 1983, the M.S.E.E. degree fromthe State University of New York, Stony Brook, in1985, and the Ph.D. in electrical engineering from theUniversity of California, Los Angeles, in 1989.

He was a Research Scientist at the NTT Basic Re-search Laboratories, Musashino, Japan, from 1989 to1992. In 1992, he became an Associate Professor inthe Electrical Engineering Department, NCKU, and

was promoted to Full Professor in 1998. Currently, he also serves as the Di-rector of the Semiconductor Research Center at NCKU. He was a Royal So-ciety Visiting Scholar at the University of Wales, Swansea, U.K., from January1999 to March 1999, a Visiting Scholar at the Research Center for AdvancedScience and Technology, University of Tokyo, Tokyo, Japan, from July 1999to February 2000, a Visiting Scholar with the Institute of Microstructural Sci-ence, National Research Council, Ottawa, ON, Canada, from August 2001 toSeptember 2001, and a Visiting Scholar with the Institute of Physics, StuttgartUniversity, Stuttgart, Germany, from August 2002 to September 2002, He is alsoan Honorary Professor of Changchun University of Science and Technology,China. His current research interests include semiconductor physics and opto-electronic devices.

C. S. Chang received the B.S. degree from the De-partment of Electrical Engineering, National ChengKung University (NCKU), Tainan, Taiwan, R.O.C.,in 2000 and the M.S. degree from the Institute ofMicroelectronics, NCKU, in 2002. Currently, he ispursuing the Ph.D. degree on the nitride-based com-pound semiconductors and optoelectrical devices atthe Institute of Microelectronics, NCKU.

Y. K. Su (SM’91) was born in Kaohsiung, Taiwan,R.O.C., on August 23, 1948. He received the B.S. andPh.D. degrees in electrical engineering from NationalCheng Kung University (NCKU), Tainan, Taiwan.

From 1979 to 1983, he was with the Departmentof Electrical Engineering, NCKU, as an AssociateProfessor and was engaged in research on compoundsemiconductors and optoelectronic materials. In1983, he was promoted to Full Professor in theDepartment of Electrical Engineering. From 1979 to1980 and 1986 to 1987, he was on leave, working at

the University of Southern California, Los Angeles, and AT&T Bell Laborato-ries, Murray Hill, NJ, as a Visiting Scholar. He was also a Visiting Professorat Stuttgart University, Stuttgart, Germany, in 1993. In 1991, he became anAdjunct Professor at the State University of New York, Binghamton. Now, he isa Professor in the Department of Electrical Engineering at NCKU and DirectorGeneral of the Department of Engineering and Applied Science, National Sci-ence Council. His research activities have been in compound semiconductors,integrated optics, and microwave devices. He has published over 200 papers inthe area of thin-film materials and devices, and optoelectronic devices.

Dr. Su is a member of SPIE, the Materials Research Society, and Phi Tau Phi.He received the Outstanding Research Professor Fellowship from the NationalScience Council (NSC), R.O.C., during 1986 to 1992 and 1994 to 1995. He alsoreceived the Best Teaching Professor Fellowship from the Ministry of Educa-tion, R.O.C., in 1992. In 1995, he received the Excellent Engineering ProfessorFellowship from the Chinese Engineering Association. In 1996 and 1998, he re-ceived the Award from the Chinese Electrical Engineering Association. In 1998,he also received the Academy Member of Asia-Pacific Academy of Materials(APAM).

CHANG et al.: NITRIDE-BASED FLIP-CHIP ITO LEDs 277

C. T. Lee (SM’97) was born in Taoyuan, Taiwan,R.O.C., on November 1, 1949. He received the B.S.and M.S. degrees in electrical engineering from theNational Cheng Kung University, Tainan, Taiwan, in1972 and 1974, respectively. He received Ph.D. de-gree in electrical engineering from Carnegie-MellonUniversity, Pittsburgh, PA, in 1982.

He worked at the Chung Shan Institute of Scienceand Technology, before he joined the Instituteof Optical Sciences, National Central University,Chung-Li, Taiwan, as a Professor in 1990. He

transferred to the Electrical Engineering Department of National Cheng-KungUniversity as the Dean of the College of Electrical Engineering and ComputerScience in 2003. His current research interests include theory, design, andapplication of guided-wave structures and devices for integrated optics andwaveguide lasers. His interest has also been involved in the research concerningsemiconductor lasers, blue light-emitting diodes, photodetectors and high-speedelectronic devices, and their associated integration for electro-optical integratedcircuits.

Dr. Lee received the Outstanding Research Professor Fellowship from theNational Science Council (NSC) of the Republic of China from 1999 until now.He received the optical engineering medal from the Optical Engineering Societyof the Republic of China in 2002 and the Distinguished Electrical EngineeringProfessor Award from the Chinese Electrical Engineering Society in 2003.

W. S. Chen was born in Chia-Yi city, Taiwan,R.O.C., in 1977. He received the B.S. degree inelectrical engineering from National Cheng KungUniversity (NCKU), Tainan, Taiwan, in 2001 and theM.S. degree from the Institute of Microelectronics,NCKU, in 2003, where he is currently pursuing thePh.D. degree in nitride-based optoelectric devices

C. F. Shen was born in Yun-Lin County, Taiwan,R.O.C, in 1981. He received the B.S. degree inelectrical engineering from National Cheng KungUniversity (NCKU), Tainan, Taiwan, in 2003. He iscurrently pursuing the M.S. degree in nitride-basedcompound semiconductors in the Institute of Micro-electronics, NCKU.

Y. P. Hsu was born in Yun-Lin County, Taiwan,R.O.C., in 1975. He received the B.S. and M.S.degrees in electrical engineering from NationalCheng Kung University (NCKU), Tainan, Taiwan,in 1998 and 2002, respectively. He is currently pur-suing the Ph.D. degree in nitride-based compoundsemiconductors in the Institute of Microelectronics,NCKU.

S. C. Shei received the B.S., M.S., and Ph.D. degreesin electrical engineering from National Cheng KungUniversity, Tainan, Taiwan, R.O.C., in 1988, 1990,and 1995, respectively. His major field is focused onIII–IV optoelectrical semiconductors.

Currently, he is the R&D Associate Vice Presidentwith the South Epitaxy Corporation, Tainan ScienceBased Industrial Park, Tainan County, Taiwan.

H. M. Lo was born in Ping-Dong, Taiwan, R.O.C., in1978. He received the B.S. degree in electrical engi-neering, Far East College, Tainan County, Taiwan, in2001.

Currently, he is the R&D Engineer with the SouthEpitaxy Corporation, Tainan Science Based Indus-trial Park, Tainan County, Taiwan.