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nologies. The MOCVD method can be used for the relatively cheap fabrication of so- phisticated layer structures with desirable bandgaps and optimized composition and Light-Emitting Diodes: doping profiles. These layered structures are the key element of electroluminescent chips. High rates of light-generation are achieved by confining the injected electrons Progress in Solid- and holes in double heterostructures and single or multiple quantum wells. Other layers are employed for contacts and cur- State rent spreading in the light-emitting layers. Another crucial issue for high-brightness LEDs is improving their light-extraction Artu¯ras Zˇukauskas, Michael S. Shur, efficiency. Providing for the efficient escape of photons from high-refractive-index and Remis Gaska materials used for light-generation is an important goal of LED chip design. The photons may escape only at incident angles smaller than the critical angle of the total Introduction internal reflection. This critical angle is 1 Until the beginning of the 19th century, problems of low light output and limited given by Snell’s law, c sin (ne/ns), flame produced by was the color range that previously precluded where ne and ns are the refractive indices only source of artificial light. Since then, LED applications in lighting. The bright- of the encapsulating epoxy resin and the physical phenomena other than pyrolumi- ness, efficiency, and color choices of LEDs semiconductor, respectively. The solution nescence have been used to produce light.1 have achieved a level that is leading to widely used at present is to clad the light- Limelight ( of calcium oxide dramatic changes in lighting technology. emitting layer with thick, transparent heated by the flame from an In this article, we review the present window layers.5,6 blowpipe), gas mantles (candoluminescence status of solid-state lighting, including dis- Figure 1 demonstrates the difference of gas-flame-heated rare-earth oxides), and cussions of the concept of high-brightness between a conventional LED and a high- the electrical Jablochkoff (an early LEDs, materials systems and chip design brightness LED. In a conventional LED type of carbon-) were among the for monochrome LEDs, white LED lamps, (Figure 1a), light generated at a certain important milestones that led to modern and, finally, the emerging applications of point in the active layer may only escape lighting technology. In the 21st century, solid-state lighting. upward through a cone with an apex of most of the residential lighting worldwide A more detailed discussion of many is- 2 c. Almost all of the light emitted in other is provided by tungsten incandescent sues related to solid-state lighting may be directions is totally reflected and absorbed lamps. Compact fluorescent lamps are also found in our upcoming book.4 in the substrate and/or in the active layer. actively promoted because of their higher Ideally, the best performance would be performance—a broader spectrum for High-Brightness LEDs achieved in a spherical LED. In practical higher-quality white light and elimination The development of high-brightness planar high-brightness LEDs, thick window of 100–120-Hz flickering, for example. LEDs relied on the introduction of new layers allow the light to escape through six Most work environments employ fluores- semiconductors with efficiencies of visible cones (see Figure 1b). The thick window cent tubes for general lighting, and street emission much higher than those of early layers allow the light generated at the cen- lighting is dominated by sodium lamps.2 LED materials, such as GaAsP (red), GaP ter of the chip to escape through the lateral Lighting consumes 2000 TWh of energy (yellow-green), and SiC (blue). Semicon- conical paths. Most commercial high- annually, about 21% of the global con- ductors used for high-brightness LEDs brightness LEDs exhibit light-extraction sumption of electricity.3 However, during must exhibit direct transitions with high efficiencies somewhat below 30%. In order the past 20 years, none of the conventional rates of radiative recombination, have to improve the light-extraction efficiency lighting technologies has exhibited a sig- wide bandgaps to emit at visible (or, in further, the LED design can employ non- nificant improvement in efficiency. The certain cases, UV) wavelengths, and pos- rectangular geometries,7 textured surfaces,8 drive to save lighting energy and reduce sess a low density of nonradiative re- and encapsulants with a higher refractive its negative environmental impact (i.e., combination centers and high durability. index (at present, epoxy resins with ne 1.6 carbon emissions and the disposal of mer- Novel Group III–V direct-gap ternary and are used). cury contained in discharge lamps) stimu- quaternary compounds and alloys have Advanced solutions for the light- lates the search for new, efficient sources met these requirements. Practical high- extraction problem rely on photon-mode of light. brightness LEDs rely on three semiconduc- engineering. In order to inhibit the gen- This search focused attention on light- tor materials systems: AlGaAs, AlGaInP, eration of light in unfavorable directions, emitting diodes (LEDs), which, prior to and AlInGaN. microcavities,9 photonic crystals (i.e., struc- the last decade of the 20th century, were High-quality compound semiconductors tures with a periodic pattern of the refractive used only as indicator lamps and numerical became available as a result of advances index),10 and emitters with surface-plasmon displays in electronic devices. Today, ma- in epitaxy and especially heteroepitaxy enhancement11 have been introduced. ture methods for fabricating compound- technology. Vapor-phase epitaxy (VPE), semiconductor materials, progress in LED liquid-phase epitaxy (LPE), and metal- AlGaAs Red LEDs design, and the emergence of blue organic chemical vapor deposition The first high-brightness LEDs were de- AlInGaN-based LEDs have resolved the (MOCVD) have all become mature tech- signed for the red spectral region using

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grown by hydride VPE (HVPE) following MOCVD growth of an AlGaInP double heterostructure on the absorbing GaAs substrate. Then the absorbing GaAs sub- strate is removed from the grown hybrid AlGaInP/GaP structure using conven- tional selective chemical etching, and, fi- nally, a GaP wafer is fused to the revealed AlGaInP layer.16 The highest performances of AlGaInP/ GaP LEDs are achieved using chips that deviate from a conventional rectangular Figure 2. Typical chip structure for shape. A truncated inverted pyramid (TIP) a high-brightness AlGaAs double- shape, which is achieved by dicing a chip heterostructure LED chip using a with a beveled blade to yield side-wall transparent substrate (after 7 Reference 12). angles of 35 with respect to the vertical, greatly improves light-extraction (Figure 3). Such a shape totally redirects internally the reflected photons at small incidence 10 lm/W, which is still three times higher angles that fit the escape cones. As of this than that of a red-filtered incandescent writing, the AlGaInP TIP LED holds the lamp. performance record for an electrolumines- Shifting the emission spectra toward cent visible-light source. In the orange shorter red wavelengths requires an active region (610 nm), it exhibits the highest layer with a wider bandgap and, hence, reported luminous efficiency, exceeding with a higher Al molar fraction. However, 100 lm/W (close to that of sodium lamps) increasing the Al content makes the direct- with a peak luminous flux of 60 lm. In gap and indirect-gap transitions closer, the red region (650 nm), external quantum which results in reduced performance. efficiencies of as high as 55% have been This makes it difficult to match the red achieved. Figure 1. (a) Schematic illustration color with the spectral sensitivity of the of the design of a conventional human eye. Another disadvantage of Blue, Green, and Amber light-emitting diode (LED) chip grown AlGaAs is its low corrosion resistance, on an absorbing substrate. Light InGaN LEDs escapes upward through a single cone which limits LED lifetime, especially under The InxGa1xN alloy exhibits a direct conditions of increased temperature and with an apex of 2c. (b) High-brightness bandgap that varies from 1.89 eV to 3.4 eV, LED chip design with thick, transparent humidity. depending on the In molar fraction. This window layers. Light escapes through covers the spectral range from red to near- six cones. Red, Orange, and Yellow UV. At present, the AlInGaN system offers AlGaInP LEDs the most efficient LEDs in the blue to 17 The (AlxGa1x)0.5In0.5P alloy, which is green region. AlGaN/GaN/AlInGaN/ lattice-matched to GaAs and exhibits a InGaN-based blue LEDs are indispensable AlGaAs/GaAs materials.12 The main ad- direct bandgap in the range of 1.9–2.26 eV for the fabrication of white LEDs (see the vantage of the AlGaAs/GaAs system is (depending on the Al molar fraction), is next section). its very small lattice mismatch (GaAs and the most favorable material for red to yel- For many years, the development of AlAs differ in lattice constant by 0.2% at low high-brightness LEDs.13 The MOCVD Group III-nitride materials was hindered 25C). This ensures the growth of high- growth of AlGaInP is a mature epitaxial by the lack of a suitable substrate. How- quality AlGaAs films on GaAs substrates. technique. Unfortunately, LPE and VPE ever, the pioneering work of Pankove, LPE can produce the thick, transparent methods, which are suitable for growing Akasaki, Nakamura, and many others led layers (having a sufficiently high Al con- thick window layers, are incompatible the way to the development of a mature tent) required for light-extraction through with the growth of AlGaInP alloys. technology for nitride MOCVD growth multiple escape cones. By using only the MOCVD technique, A typical high-brightness AlGaAs LED the structure of high-brightness AlGaInP chip consists of a double-heterostructure LEDs can be optimized by inserting a active layer sandwiched between thick current-blocking layer under the top con- (30–120 m) wide-bandgap layers that tact and introducing a distributed Bragg simultaneously serve as injection and con- reflector between the absorbing GaAs sub- fining layers (see Figure 2). After the strate and the light-emitting structure.14 structure is grown, the absorbing GaAs The reported of such substrate is removed in order to allow the LEDs is 26 lm/W at 590 nm (an external generated light to escape in the down- quantum efficiency of 5%).15 ward direction. A much better performance is achieved AlGaAs LEDs can feature external quan- by combining MOCVD with other tech- tum efficiencies of up to 21% at 650 nm nologies (VPE and wafer-bonding) to pro- Figure 3. Vertical cross section of (15 lm/W). Commercial devices exhibit a duce thick, conductive (heavily doped) a truncated inverted pyramid (TIP) somewhat lower performance, around GaP windows. The upper window layer is AlGaInP/GaP LED (after Reference 7).

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over substrates that are mismatched in White LEDs epoxy resin and phosphor particles. The lattice constants and coefficients of ther- Creating an efficient and practical whole structure is embedded in trans- mal expansion. The most extensively used source of white light is the ultimate goal of parent resin. At present, the most efficient substrate is sapphire (Al2O3, 15% lattice solid-state lighting technology. The most phosphor used in white dichromatic LEDs 3 mismatch); its success is attributable to the challenging application for white LEDs is is (Y1aGda)3(Al1bGab)5O12 Ce garnet with introduction of low-temperature AlN18 and the replacement of conventional incandes- optimized excitation and emission spec- GaN19 buffer layers. The breakthrough in cent and fluorescent lamps. Practical white tra. Using this formulation, white, dichro- epitaxial growth of III–N materials, as well LEDs became feasible with the availability matic, phosphor-conversion LEDs with an as the demonstration of low-resistivity of high-brightness AlInGaN emitters.17 efficiency of 15 lm/W and color rendering p-type GaN,20 allowed for the develop- Based on blue and UV LEDs, white solid- somewhat below 80 points are being manu- ment of a high-brightness InGaN/Al2O3 state lamps that exploit additive mixing of factured. An efficiency of 50 lm/W is ex- LED.21 Light-emitting InGaN structures two or more colors have been developed. pected in the near future. For comparison, have also been grown on 6H-SiC (3.5% There are basically two ways to produce the efficiencies of conventional lighting 22 mismatch) and spinel (MgAl2O4, 9.5% white light by LEDs. The first is to down- devices are 14 lm/W for incandescent mismatch).23 All of these substrates are convert a part of the emission from a lamps (60 W), 50 lm/W for compact fluo- transparent to the light generated in the blue chip, or light from a UV chip, to a rescent lamps (15 W), and 80 lm/W for LEDs. Transparent substrates and the rela- longer-wavelength light using phosphors fluorescent tubes (32 W). However, tively low refractive index of InGaN (2.5, (phosphor-conversion LEDs). The other garnet-based white LEDs exhibit reduced in comparison with 3.4 for GaP) are the way is to mix light of different colors efficiency caused by the Stokes shift char- reasons for the efficient light-extraction emitted by a few primary chips (multichip acteristic of down-conversion and suffer demonstrated by nitride LEDs.24 For top- LEDs). from reduced lifetime due to phosphor emitting devices, luminous efficiencies The most efficient dichromatic system deterioration.29 (external quantum efficiencies) of 7 lm/W employs sources with a peak wavelength Improved efficiency and color render- (14%) for blue (465 nm), 60 lm/W (11%) of about 440 nm and 570–590 nm. How- ing are offered by a trichromatic design for green (525 nm), and 21 lm/W (4.5%) ever, lighting applications require not only for the phosphor-conversion LED. The for amber (595 nm) LEDs have been a high luminous efficiency but also good optimal combination of primary sources achieved.25 color rendering (i.e., suitably composed (450/540/610 nm) may be implemented Less efficient but potentially cheaper broad spectra that enable one to properly by using partially absorbed blue light GaN/InGaN-based LEDs on silicon sub- distinguish the colors of illuminated ob- from an InGaN chip and two appropriate strates have been demonstrated as well.26 jects). The color-rendering ability of a light phosphors for the green and orange re- 2 A promising approach for the develop- source is characterized by the general color- gions. For instance, an ionic SrGa2S4 Eu ment of nitride LEDs is strain-energy rendering index (CRI) Ra, which varies phosphor can serve for the conversion of 2 band engineering based on quaternary from 0 to 100 points. Values of Ra above blue light to green and a SrS Eu phos- AlGaInN alloys.27 80 points correspond to “deluxe” color phor for the conversion of blue light to Since the value of the refractive index of rendering. orange.30 A UV-LED-based white lamp sapphire (1.8) is between those for InGaN A dichromatic, phosphor-conversion with three different phosphors that produce and the epoxy resin that encapsulates the white LED was designed using an InGaN a quasi-continuous emission spectrum has LED chip, some light that is totally reflected chip that emits blue light and a phosphor been proposed.31 from the top surface escapes through the that absorbs a part of this light and emits Multichip white LEDs should have a substrate. As a result, a major part of the in the yellow region. Figure 5 depicts a higher efficiency due to the absence of 17 emission from the InGaN/Al2O3 chip is typical design of such a device. The blue energy losses caused by the Stokes shift directed downward. Hence, it is reasonable chip is mounted in a reflector cup and and nonradiative recombination in the to flip the chip in order to improve the coated with a converter layer, a mixture of phosphor. Also, aging problems related to performance. Figure 4 depicts a schematic the phosphor are avoided. The simplest cross section of a high-power flip-chip implementation of a trichromatic white- InGaN LED that exhibits a wall-plug effi- emitter is a package with three single ciency (ratio of optical power to input LEDs (red, green, and blue), similar to that electrical power) of 20% and a peak light used for full-color video screens.32 Further output of 400 mW.28 advances in white multichip LEDs might be achieved by heterointegration of semi- conductor LEDs into a single epitaxial structure, for instance, by selective-area MOCVD.26 Since LEDs emit narrow spec- tral lines, more than three primary sources might be required for high values of color- rendering. Figure 6 depicts optimal spec- tra of white multichip lamps composed of 2–5 LEDs.33 The dichromatic lamp is seen to be sensible only for the highest luminous output with color rendering close to zero. The trichromatic and quadrichromatic Figure 5. Schematic structure lamps cover the entire range of reasonable of an InGaN-based dichromatic, general CRI values. The quintichromatic Figure 4. Chip structure of a high-power phosphor-conversion white LED lamp can generate a supreme-quality InGaN flip-chip LED (after Reference 28). (after Reference 17). quasi-continuous spectrum that might

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Large full-color video displays are the directionality, compactness, reduced fire major monochrome application of high- hazard, low operating voltages, and robust- brightness LEDs. Installations first emerged ness are required. For example, such illumi- in downtown Tokyo and New York City nation is required for outlining the contours soon after the appearance of InGaN green of buildings and other structures for deco- and blue LEDs. Later, huge LED screens rative and advertising purposes. Contoured found many applications in advertising, lighting systems made of LED chains and and they are quickly becoming an integral LED-backlighted plastic tubes are gradu- feature of entertainment arenas and sports ally replacing neon tubes. Other examples stadiums. Typically, a large video display are low-wattage security and landscape contains 107 LEDs.36 LED-based alpha- lighting, small , and spotlights for numeric displays, such as variable message museum or gallery applications and for signs, are also widely used. highlighting merchandise on store shelves. High-brightness LEDs that efficiently The largest potential application for white convert electrical energy to narrow-band LEDs is general lighting. A revolution in radiation and have unsurpassed longevity general lighting may occur in the next are the most advanced technology in power decade, when white LEDs are expected to signage. A good example of their applica- attain an efficiency of 100–200 lm/W and tion is as replacement lamps for traffic a luminous flux per package of 100 lm.34 lights. The tenfold improvement in lumi- Solid-state lamps are rapidly penetrating nous efficiency of red, amber, and green fields such as medical applications, optical LEDs in comparison with filtered incan- measurements, and photosynthesis. LEDs descent lamps results in a payback period were shown to emit a radiant flux high of less than one year. Also, because of the enough for phototherapy of neonatal jaun- LEDs’ longer lifetime, maintenance costs dice, photodynamic therapy, and dental- Figure 6. Optimized spectral power are reduced, and the traffic flow is dis- composite curing.4 Owing to their high distributions for multichip lamps turbed less often. Finally, traffic safety in- output power, low noise, ability to generate composed of (a) 5, (b) 4, (c) 3, and creases, since the LED lamps do not reflect subnanosecond pulses, and their simple (d) 2 primary LEDs. K is the luminous efficacy (i.e., the imaginable sunlight, experience no sudden failure, means of high-frequency modulation, blue performance for 100% quantum and are sturdy enough to withstand van- and UV LEDs can replace costly in efficiency of the LEDs) and Ra is dalism. Other power-signage applications some applications of excita- the general color-rendering index are exit signs, safety beacons (e.g., solar- tion, including time-resolved measure- (after Reference 33). powered marine lights), roadway cross- ments. Plant growth under completely walk warning systems, and airport runway solid-state lighting using red AlGaAs and lighting. blue InGaN chips has been demonstrated.37 satisfy the lighting needs of individuals Automotive signage offers a tremendous We would like to conclude this article with color-perception defects, since they market for high-brightness LEDs. LED by quoting one of the pioneers of the LED require a more continuous spectrum in lighting was introduced years ago in center revolution, Prof. Nick Holonyak Jr. of the order to distinguish colors. high-mounted brake lights. Soon the entire University of Illinois, who stated, “. . . it is Multichip LEDs composed of the most tail-light section of the car may incorpo- vital to know that the LED is an ultimate efficient planar chips available at present rate AlGaInP red and orange LEDs. Most form of lamp, in principle and in practice, (50% external quantum efficiency for red of the car manufacturers are using LEDs and that its development indeed can and and yellow AlGaInP-based LEDs7 and 20% for instrument-panel lighting and interior will continue until all power levels and for blue and green AlInGaN-based LEDs28) illumination. The advantages of LED colors are realized.”38 might surpass the efficiency of any con- lighting in automotive applications are a ventional source of white light. long lifetime (no maintenance is required Acknowledgment throughout the lifetime of a car) and high The work of Dr. A. Zˇ ukauskas was par- Applications shock resistance (in contrast to incandes- tially supported by the National Research Their high luminous efficiency and lu- cent lamps, LEDs may be mounted on the Council’s Twinning Program. minous flux allow high-brightness LEDs trunk lid and can withstand slamming to compete with conventional light sources when switched on). While the switch time References 34 1. B. Bowers, Lengthening the Day: A History of for many applications. The relatively of incandescent lamps is 0.1 s, LED brake Lighting Technology (Oxford University Press, high cost of LED lamps is partially com- lights switch on instantaneously, which Oxford, 1998). pensated by their superior lifetime, typi- improves driver response time when the 2. J.R. Coaton and A.M. Marsden, eds., Lamps cally 100,000 h in comparison with vehicle ahead slows. The compactness of and Lighting (Arnold, London, 1997). 800–5000 h for incandescent bulbs and LEDs saves space and reduces vehicle 3. A. Lidow, in Proc. APEC’99—14th Annu. Ap- 10,000–20,000 h for fluorescent tubes. weight. Also, the reduced energy consump- plied Power Electronics Conf., Vol. 1 (Institute of Since the cost per unit of luminous flux is tion of LED lights allows for the use of a Electrical and Electronics Engineers, Piscataway, NJ, 1999) p. 10. continually decreasing, the number of pos- smaller generator. Their negligible heating ˇ sible applications is expected to increase allows the use of inexpensive plastic op- 4. A. Zukauskas, M.S. Shur, and R. Gaska, In- troduction to Solid-State Lighting (J. Wiley and dramatically in the near future. At present, tics. As a result, as many as 1000 LEDs 37 Sons, New York) to be published. LEDs are beginning to dominate in mono- might be used in a single car. 5. G.B. Stringfellow and M.G. Craford, eds., High chrome lighting applications, and some Colored and white LEDs are being used Brightness Light Emitting Diodes, Semiconductors white illumination applications have al- in low-power lighting applications where and Semimetals, Vol. 48 (Academic Press, New ready emerged.35 maintenance cost is significant and/or York, 1997).

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6. S.J. Lee, Jpn. J. Appl. Phys., Part 1 37 (1998) Shen, C. Lowery, P.S. Martin, S. Subramanya, He can be reached by e-mail at p. 509. W. Götz, N.F. Gardner, R.S. Kern, and S.A. [email protected]. 7. M.R. Krames, M. Ochiai-Holcomb, G.E. Höfler, Stockman, Appl. Phys. Lett. 78 (2001) p. 3379. C. Carter-Coman, E.I. Chen, I.-H. Tan, P. Grillot, 29. N. Narendran, N. Maliyagoda, A. Bierman, Michael Shur is the Patricia W. and N.F. Gardner, H.C. Chui, J.-W. Huang, S.A. R. Pysar, and M. Overington, in Proc. SPIE, C. Sheldon Roberts ’48 Professor of Solid-State Stockman, F.A. Kish, M.G. Craford, T.S. Tan, Light-Emitting Diodes: Research, Manufacturing, C.P. Kocot, M. Hueschen, J. Posselt, B. Loh, and Applications IV, Vol. 3938, edited by H.W. Electronics at RPI. He is also professor of G. Sasser, and D. Collins, Appl. Phys. Lett. 75 Yao, I.T. Ferguson, and E.F. Schubert (SPIE— physics, applied physics, astronomy, and (1999) p. 2365. The International Society for Optical Engineer- information technology and associate director 8. R. Windisch, B. Dutta, M. Kuijk, A. Knobloch, ing, Bellingham, WA, 2000) p. 240. of the Center for Integrated Electronics and S. Meinlschmidt, S. Schoberth, P. Kiesel, G. 30. R. Mueller-Mach and G.O. Mueller, in Proc. Electronics Manufacturing at RPI. Borghs, G.H. Dohler, and P. Heremans, IEEE SPIE, Light-Emitting Diodes: Research, Manufac- Shur received an MSEE degree (with Trans. Electron Devices 47 (2000) p. 1492. turing, and Applications IV, Vol. 3938, edited by honors) from St. Petersburg Electrotechnical 9. E.F. Schubert, N.E.J. Hunt, M. Micovic, R.J. H.W. Yao, I.T. Ferguson, and E.F. Schubert Institute and his PhD and DSci degrees in Malik, D.L. Sivco, A.Y. Cho, and G.J. Zydzik, (SPIE—The International Society for Optical physics and mathematics from the Ioffe Science 265 (1994) p. 943. Engineering, Bellingham, WA, 2000) p. 30. 10. T.F. Krauss and R.M. De La Rue, Progr. 31. D. Eisert, U. Strauss, S. Bader, H.-J. Lugauer, Physico-Technical Institute in St. Petersburg, Quantum Electron. 23 (1999) p. 51. M. Fehrer, B. Hahn, J. Baur, U. Zehnder, N. Stath, Russia. He has held research or faculty 11. J. Vucˇkovic´, M. Loncˇar, and A. Scherer, IEEE and V. Härle, Inst. Pure Appl. Phys. Conf. Ser. 1 positions at various universities, including J. Quantum Electron. 36 (2000) p. 1131. (2000) p. 841. the Ioffe Institute, Cornell University, the 12. F.M. Steranka, in High Brightness Light Emit- 32. G. Bogner, A. Debray, G. Heidel, K. Hoehn, University of Minnesota, and the University ting Diodes, Semiconductors and Semimetals, U. Mueller, and P. Schlotter, in Proc. SPIE, Light- of Virginia, where he was John Money Vol. 48, edited by G.B. Stringfellow and M.G. Emitting Diodes: Research, Manufacturing, and Ap- Professor of Electrical Engineering and Craford (Academic Press, New York, 1997)p. 65. plications III, Vol. 3621, edited by E. Schubert, I.T. served as director of the Applied 13. F.A. Kish and R.M. Fletcher, in High Bright- Ferguson, and H. Yao (SPIE—The International Electrophysics Laboratories. ness Light Emitting Diodes, Semiconductors and Society for Optical Engineering, Bellingham, Semimetals, Vol. 48, edited by G.B. Stringfellow WA, 1999) p. 143. He is a fellow of IEEE and the and M.G. Craford (Academic Press, New York, 33. F. Ivanauskas, R. Vaicekauskas, A. Zˇukauskas, American Physical Society; a member of the 1997) p. 149. M.S. Shur, and R. Gaska, “Optimization of the Electrochemical Society, the Electromagnetic 14. H. Sugawara, K. Itaya, H. Nozaki, and G. Parameters of White Polychromatic Light Emit- Academy, the Materials Research Society, Hatakoshi, Appl. Phys. Lett. 61 (1992) p. 1775. ting Diode,” presented at the 6th Int. Conf. on SPIE, and the American Society for 15. S.W. Chiou, C.P. Lee, C.K. Huang, and C.W. Mathematical Modeling and Analysis, Vilnius, Engineering Education; and an elected Chen, J. Appl. Phys. 87 (2000) p. 2052. June 2001. member and former chair of U.S. Commission 16. F.A. Kish, F.M. Steranka, D.C. DeFevere, 34. R. Haitz, F. Kish, J. Tsao, and J. Nelson, Com- D of the International Union of Radio Science D.A. Vanderwater, K.G. Park, C.P. Kuo, T.D. pound Semicond. 6 (2) (2000) p. 34. (URSI). In 2001, he was elected member-at- Osentowski, M.J. Peanasky, J.G. Yu, R.M. 35. M.W. Hodapp, in High Brightness Light Fletcher, D.A. Steigerwald, M.G. Craford, and Emitting Diodes, Semiconductors and Semimetals, large of the U.S. National Committee of URSI V.M. Robbins, Appl. Phys. Lett. 64 (1994) p. 2839. Vol. 48, edited by G.B. Stringfellow and M.G. (USNC URSI). Shur is editor-in-chief of the 17. S. Nakamura and G. Fasol, The Blue Craford (Academic Press, New York, 1997) p. 227. International Journal of High-Speed Diode: GaN Based Light Emitters and Lasers 36. B. Schweber, “Blue LEDs, Digital TV Electronics and Systems, editor of a book (Springer, Berlin, 1997) p. 343. Bring Daylight-Bright Signs to Masses,” EDN series on special topics in electronics and 18. H. Amano, N. Sawaki, I. Akasaki, and Y. No. 8 (2000) p. 56, available from http:// systems published by World Scientific, and a Toyoda, Appl. Phys. Lett. 48 (1986) p. 353. www.ednmag.com. member of the Honorary Board of Solid-State 19. S. Nakamura, Jpn. J. Appl. Phys., Part 2: Lett. 37. K. Okamoto, T. Yanagi, S. Takita, M. Tanaka, Electronics. From 1990 to 1993, he served as 30 (1991) p. L1705. T. Higuchi, Y. Uchida, and H. Watanabe, Acta an associate editor of IEEE Transactions on Hortic. 440 (1996) p. 111. 20. S. Nakamura, N. Iwasa, M. Senoh, and T. Electron Devices. Shur has served as chair, Mukai, Jpn. J. Appl. Phys., Part 1 31 (1992) p. 1258. 38. N. Holonyak Jr., Am. J. Phys. 68 (2000) p. 864. program chair, and member of the organizing 21. S. Nakamura, T. Mukai, and M. Senoh, ˇ Appl. Phys. Lett. 64 (1994) p. 1687. Artu¯ ras Zukauskas is Chief Research and program committees for many IEEE 22. Y. Kuga, T. Shirai, M. Haruyama, H. Worker at the Institute of Materials Science conferences. He is one of co-developers of Kawanishi, and Y. Suematsu, Jpn. J. Appl. Phys., and Applied Research within Vilnius University AIM-Spice, a version of the analog circuit Part 1 34 (1995) p. 4085. in Lithuania, and is also a professor in the simulator SPICE. In 1994, the St. Petersburg 23. J.W. Yang, Q. Chen, C.J. Sun, B. Lim, M.Z. Department of Semiconductor Physics at the State Technical University awarded him an Anwar, M.A. Khan, and H. Temkin, Appl. Phys. university. Currently, his research group is honorary doctorate. He is also a co-author of Lett. 69 (1996) p. 369. engaged in fundamental investigations of the paper that received the best paper award 24. S.J. Lee, Jpn. J. Appl. Phys., Part 1 37 (1998) carrier relaxation and recombination in highly at GOMAC–98 and a co-author of a best p. 5990. 25. T. Mukai, M. Yamada, and S. Nakamura, photoexcited direct-gap semiconductors, poster paper award from MRS. In 1999, Jpn. J. Appl. Phys., Part 1 38 (1999) p. 3976. optical characterization of materials for Shur received the van der Ziel Award 26. J.W. Yang, A. Lunev, G. Simin, A. Chitnis, optoelectronics (mostly AlInGaN systems), from ISDRS-99 and a Commendation for M. Shatalov, M.A. Khan, J.E. Van Nostrand, and and applications of solid-state lamps. Excellence in Technical Communications R. Gaska, Appl. Phys. Lett. 76 (2000) p. 273. Zˇ ukauskas received a PhD (candidate) from Laser Focus World. In 2000, he was 27. A. Chitnis, A. Kumar, M. Shatalov, V. degree in semiconductors and dielectrics in listed as one of the most quoted researchers Adivarahan, A. Lunev, J.W. Yang, G. Simin, 1983 and a habilitation doctorate in natural in his field. M.A. Khan, R. Gaska, and M. Shur, Appl. Phys. sciences in 1991, both from Vilnius University. Shur can be reached by e-mail at Lett. 77 (2000) p. 3800; M. Shatalov, A. Chitnis, In 2000–2001, he was a visiting scientist at [email protected] and via URL V. Adivarahan, A. Lunev, J. Zhang, J.W. Yang, Q. Fareed, G. Simin, A. Zakheim, M.A. Khan, Rensselaer Polytechnic Institute (RPI) in http://nina.ecse.rpi.edu/shur/. R. Gaska, and M.S. Shur, Appl. Phys. Lett. 78 Troy, N.Y. (2001) p. 817. He is a member of the Lithuanian Materials Remis Gaska is a research associate 28. J.J. Wierer, D.A. Steigerwald, M.R. Krames, Research Society and an expert member of the professor in the Electrical, Computer, and J.J. O’Shea, M.J. Ludowise, G. Christenson, Y.-C. Lithuanian Academy of Science. Systems Engineering Department at RPI.

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In 1999, he co-founded Sensor Electronic Technology Inc., where he is now president and CEO. His research interests include wide- Atoms are the floating part of all material, the part bandgap III–nitride semiconductor materials that makes you sit up suddenly and, smiling, say: “Y“Youou know, suddenly, and devices and A2B6- and A4B6-based electronic and optoelectronic devices on for some reason, I feel like going for a swim!” Actually the space in flexible substrates. Gaska received his MS and PhD degrees in which atoms drift is dry, I only said that because they have this concept physics from Vilnius University and a PhD degree in electrical engineering from Wayne regarding floating. State University in Detroit, Mich. From 1981 to 1992, he was a junior research fellow, then Michael Benedikt a senior research fellow, at Vilnius University. from “The Life of Particles” In 1996, he was a research associate in the Department of Electrical Engineering at the University of Virginia. From 1997 to 1998, he worked as a senior research scientist and then R&D manager at APA Optics Inc. in Minneapolis, Minn. Gaska’s research results have been published in over 200 technical Cost-Effective Portable Spin Coaters papers and conference presentations. He received the Thomas C. Rumble Fellow award Two-Stage Spinning from Wayne State University in 1995 and a best poster paper award from MRS in 1999. • Dispense liquid during Stage 1 Gaska can be reached by e-mail at • Spin-up and flatten during Stage 2 [email protected]. Adjustable Speed Stage 1 • 500 to 2,500 rpm Advertisers in This Issue • 2 to 18 seconds Page No. Stage 2 • 1,000 to 8,000 rpm Bede Scientific, Inc. 758 KW-4A • 3 to 60 seconds Chemat Technology, Inc. 769 Digital Instruments/ Precision Video Biological Microscope Veeco Metrology Group 763 Features Electrochemical Society (ECS) 754 Only $1,968.90 • Fully Coated Optical System E-MRS/MRS 802 (including Video Camera) • 45mm Achromatic Objective, Goodfellow Corp. 755 Parfocall • Coaxial Coarse and Fine Focus High Voltage Engineering Inside front cover Adjustment Huntington Mechanical • Focusing Stops to prevent Laboratories, Inc. Outside back cover Objectives & Slides from being Damaged IUMRS/Facets 749 • Built-in Illumination, Adjustable MMR Technologies, Inc. 797 • Brightness Specifications MRS/OSA 770 • Trinocular Head for Video Camera National Electrostatics Corp. 756 XSZ-107CCD • Wide Field Eyepieces WF 10X, The Phosphor Technology 753 P16X( WF 16X) • Achromatic 4X, 10X, 40X(S) Thermionics Vacuum Products 757 and 100X(S, Oil) VAT, Inc. 759 CHEMAT TECHNOLOGY, INC. For free information about the products and services 9036 Winnetka Avenue, Northridge, CA 91324 B RS OOT offered in this issue, check www.mrs.org/publications/ M H U.S. Toll-Free 800-475-3628 • Non-U.S. 818-727-9786 IT N

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