BROADBAND WIRELESSEndwave and GigaBeam link New York’s glitterati

WiMAX offers GaNmarket opening

Extracting morelight from HB-LEDs

Lumileds re-ignitespatent litigation

ALSO INSIDE

December 2005 Volume 11 Number 11

http://www.intrinsicsemi.com

DECEMBER 2005 VOLUME 11 NUMBER 11

Analysts say existing methods are unsuitablefor categorizing warm-white light. p19

Nitronex hopes that WiMAX market growth will drive GaN-on-silicon HEMT sales. p23

Phasebridge’s fiber-optic gyroscopes give anew spin to Emcore’s product portfolio. p11

5 Headline News Lumileds ignites battle with Taiwan duo...Agilent’s semiconductor business spawns Avago Technologies...Substrate firms grab wide-bandgap funds

6 GaAs & Wireless News Motorola taps into EDGE...Endwave unveils rights plan as shares fall...Hitachi Cable voted best SI GaAs substrate vendor... RFMD employs laser dicer at GaAs fab...In brief

8 LED News Showa Denko develops a passion for bright LEDs...Holographic photonic crystals increase extraction efficiency...HB-LED suppliers top 100...Substrate impurities boost white output...Industry in need of uniform standards...In brief

11 Opto News Emcore buys gyroscope specialist Phasebridge...Brighter LEDs speed up water purification...

13 Fiber News Infinera gains as long haul improves...Firecomms reveals RCLED transceiver for in-car networks

31 M&E News Oxford has access to atomic layerpatents...Matheson reshuffles...Trikon seals merger

COMPOUND SEMICONDUCTOR DECEMBER 2005 1

On the cover: GigaBeam is switching from silicon to GaAs and InP components to increase the data transfer rate of its broadband radio transmissions. Thecover image shows a transmitter serving the residents of Trump Towers, New York, with high-speed wireless internet. Credit: GigaBeam.

NEWS

16 GigaBeam turns to III-Vs for ultra-fast broadband radioThe cost of deploying fiber to the premise limits the datarates available to most US businesses. The solution, sayDoug Lockie and Don Peck of GigaBeam, is to connectfiber networks to enterprises by millimeter-wave radiotransmissions, delivering gigabit-per-second data rates.

COVER STORY: BROADBAND WIRELESS

19 Industry must work together to displace light bulb cultureHB-LED manufacturers should concentrate on building relationships with their customers in order to break down the incumbent culture based around the Edison light bulb, say analysts.

23 WiMAX and WiBro emerge as major targets for GaNNew broadband wireless access protocols could provide amarket for GaN transistors before any significant activityfrom the third-generation cellular business appears, writesMichael Hatcher.

27 Efficiency gains boost high-power LED performanceDesigners are exploiting increasingly sophisticatedstrategies to boost efficiency and enhance light output.Susan Curtis reports.

FEATURES

Compound Semiconductor’s circulationfigures are audited by BPA International

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32 Research Review 001 silicon improves GaN integration...MOXtronics makes ZnO photodiodes and transistors...Complementary techniques offer better route to GaN-on-sapphire growth of GaN-on-sapphire epilayers

DEPARTMENTS

28 Suppliers Guide

31 Product Showcase

ADVERTISING SECTION

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US mailing information: CompoundSemiconductor (ISSN 1096-598X) is published 11 times a year for $148 by Institute of PhysicsPublishing, Dirac House, Temple Back, Bristol BS1 6BE, UK. Periodicals postage paid atMiddlesex, NJ 08846. POSTMASTER: sendaddress corrections to Compound Semiconductor,c/o PO Box 177, Middlesex, NJ 08846. US agent:Pronto Mailers Association Inc, 200 Wood Avenue,PO Box 177, Middlesex, NJ 08846.

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Advertisers’ Index

It’s the season for cell-phone handset makers and theirsuppliers to be jolly, as the public goes into retail overdrive.Usually, the Christmas holiday period is followed by a commercial hangover as credit card bills arrive and pockets aretightened. But this year RF Micro Devices (RFMD) – one ofthe III-V industry’s biggest names – is expecting the opening

quarter of calendar 2006 to be a little different.Financial chief Dean Priddy is reckoning on a strong March quarter to

follow RFMD’s traditionally buoyant end to the year. The reason could bethe company’s belief that it is taking share away from its competitors in thehigh-end handset market; or perhaps that its top customer, Nokia, iswitnessing a surge in sales of phones to China, where February marks thelocal holiday season.

What’s good for RFMD can generally be regarded as being good for thewider compounds industry, but whether that will still be the case severalyears from now is open to debate. RFMD is rightly keen to promote itself as“technology agnostic”, which means that its primary responsibility is tomake the best products for its customers, regardless of the material fromwhich its chips are made.

For the time being, GaAs will remain the material of choice for its poweramplifiers, and the company will increase its GaAs consumption next yearas it brings the production of PHEMT switches in house. But in the longrun, this could all change. The key to RFMD’s future strategy is integration.It sees future cell-phone architectures as two-chip solutions. This means onebaseband chip, supplied by the likes of Texas Instruments or Intel, and onechip to do everything else. The “everything else” chip is what RFMD wantsto supply, as it will give the company more content in each phone.

The big challenge is therefore integration. And efforts to integrate siliconwith GaAs will prove crucial if GaAs is to continue cultivating its keycommercial application in the long term.

Michael Hatcher

COMPOUND SEMICONDUCTOR DECEMBER 2005

Handset season strategies

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HEADLINE NEWS compoundsemiconductor.net

COMPOUND SEMICONDUCTOR DECEMBER 2005 5

California-based LED manufacturer LumiledsLighting is suing the Taiwanese companiesEpistar and United Epitaxy Company (UEC),alleging that the two are infringing key patentsrelating to AlGaInP devices.

“Lumileds seeks an exclusion order barringentry into the US of the accused LEDs, as wellas products containing those LEDs,” declaredthe company in a statement.

As well as filing a complaint to the USInternational Trade Commission, Lumiledsis suing Epistar and UEC at the US DistrictCourt for the Northern District of California,seeking an injunction against future infringe-ment, damages, and “enhanced damages forwillful infringement”.

The complaint is the latest twist in a litiga-tion battle that the three companies havewaged for much of the past decade (see“Patent fight timeline”).

Previous episodes in the series of lawsuitshave centered on the details disclosed in USpatent 5,008,718, entitled “LED with an elec-

trically conductive window”, which Lumiledswas granted in 1991.

The new litigation instigated by Lumiledscites the “718” patent, as well as two laterpatents (5,376,580 and 5,502,316) concern-ing a wafer-bonding technique awarded toFred Kish and colleagues at Hewlett-Packardprior to the spin-off of Agilent Technologies.

Specifically, the accusations refer to the useof omnidirectional mirror adhesion LEDs byEpistar, and metal- and glue-bonding by UEC.

1999: Lumileds states out of court that UEC infringed the “718” patent; UEC suesLumileds, saying the patent is invalid ongrounds of “obviousness”.2000: Aglient, Lumileds file a counter-claim.2001: Pending cases between UEC,Lumileds and Agilent are settled.2003: Lumileds files against Epistar, citing

infringement of the same “718” patent.2004: Pending litigation is settled whenLumileds grants Epistar a limited licence touse technology disclosed in several patentsabout absorbing-substrate AlGaInP LEDs.2005: Philips Lighting buys out Agilent’s half share in Lumileds; Epistar and UECreveal that they are planning to merge.

Patent fight timeline

Yellow and red AlGaInP LEDs made by UECuse the disputed metal-bonding process.

By Michael HatcherAgilent Technologies has completed the sell-off of its semiconductor business, which hasnow begun operations as Avago Technologies.

Equity firms Kohlberg Kravis Roberts andSilver Lake Partners have taken control of theworld’s largest privately held semiconductorcompany in completing the $2.66billion deal.

Dick Chang, who was the business’s mostrecent CEO under Agilent, retains his posi-tion at the renamed company. Chang said thatAvago would now look to capitalize on its newindependence to drive profitability.

While some media reports have claimedthat the new owners plan to make Avago a pub-

lic company once again through separate IPOsfor its different business segments, an Avagospokesman told Compound Semiconductorthat this was not true. “There is no specific planfor one or multiple IPOs,” he said. “DickChang and our new board have no such plans.”

Avago has 6500 employees, offers 5500products, raked in revenue of $1.8 billion infiscal 2005, and covers three key areas of thecompound semiconductor business.

Although Avago sees itself primarily as afabless operation, it owns three facilitieswhere it manufactures III-V devices. Theseare a 6 inch GaAs fab in Fort Collins, CO,where it makes E-PHEMT power amplifiers

for cell phones among other III-V and siliconprocesses; a 3 inch VCSEL facility in Singa-pore, which is used for volume laser produc-tion; and a smaller 3 inch VCSEL fab in SanJose, CA, primarily focused on research anddevelopment work.

Avago uses many of its optoelectronicdevices in optical mouse sensors, which canbe based on either laser diodes or LEDs. As if to emphasize its strategy to steer awayfrom semiconductors and focus on test andmeasurement, Agilent has acquired MolecularImaging, a Tempe, AZ, firm that specializes inatomic force microscopes for applicationsin nanotechnology.

Two US companies that specialize in wide-bandgap substrates have won new funding todevelop commercial products.

HexaTech, a Raleigh, NC, firm that is devel-oping AlN substrates, has won $8.9 millionfrom venture capitalists to advance its prod-uct development, expand marketing, andstrengthen its management.

Intersouth Partners led the Series Afunding,

with HIG Ventures, Sevin Rosen Funds (SVR)and NC IDEA also making contributions.Craig Burson of HIG Ventures, John Glushikof Intersouth and Dave McLean of SVR willjoin the company’s board of directors.

HexaTech was spun out of North CarolinaState University in 2001 and uses a proprietaryprocess that combines physical vapor trans-port with seeded growth to fabricate single-crystal AlN substrates.

“This [funding] will enable us to acceler-ate the scaling of our AlN wafers to commer-cially viable sizes, significantly increase our

wafer production capacity, and develop newdevices and strategic partnerships,” remarkedcompany CTO Zlatko Sitar.

Meanwhile, the giant silicon chemicalscompany Dow Corning has won $3.6 millionfrom the US Department of Defense, via theOffice of Naval Research, to develop 100mm-diameter device-quality SiC substrates.

There are plans for Dow’s compound semi-conductor solutions division to develop crys-tal growth technology along with waferingand epitaxy skills at its integrated SiC sub-strates operation in Auburn, MI.

Substrate firms grabwide-bandgap funds

Lumileds ignites battle with Taiwan duo

Agilent’s semiconductor business spawns Avago TechnologiesU

EC

By Michael HatcherThe board of directors of RF module manu-facturer Endwave Corporation has approveda share purchase rights plan, following analarming slide in the company’s stock valueover the past few months,

Endwave has introduced the plan to protectit from what it describes as “abusive” takeovertactics, although the company said the planwas not a response to any particular proposal.

Under the plan, all stockholders receivedrights to purchase a new series of preferredstock on December 12, 2005.

In July, Endwave’s share price peaked at$55.41, giving the firm a value of $627millionat the time. As the stock peaked, Endwave’sbiggest shareholder, Northrop Grumman, sold1.4 million shares in the company, worth anestimated $75.6 million.

Northrop Grumman continued to sell large

numbers of shares throughout July, includinga deal valued at $36.8 million on July 18, bywhich time the stock price had already plum-meted to $40. A flurry of activity followedin the summer, with Endwave’s senior man-agement cashing in stock options as the com-pany’s value continued to fall and NorthropGrumman sold off more of its holding. InSeptember, Endwave said that it could notexplain either the intense market activity inits stock or its price weakness.

As we went to press, Endwave was tradingat $10.50, 80% down from its summer high.Northrop Grumman remains the company’sbiggest shareholder, owning just over 10%. Endwave has signed a deal with LoeaCorporation, a subsidiary of Trex Enterprises,to work on the design of 71–86 GHz subsys-tems for use in multi-gigabit wireless systemsfor last-mile communications.

GAAS & WIRELESS NEWS

COMPOUND SEMICONDUCTOR DECEMBER 20056

Motorola taps into EDGEMotorola, the world’s second-ranked supplierof cell phones behind Nokia, has signed dealswith rival GaAs chip makers Skyworks Solu-tions and RF Micro Devices (RFMD) overnew technologies for EDGE handsets.

Skyworks and Motorola will work togetheron a next-generation radio transceiver, whichSkyworks says will allow it to more than dou-ble its addressable semiconductor content ineach mobile handset made by Motorola.

The technology is based on Skyworks’patented closed polar loop, flexible radio archi-tecture, known as the Helios DigRF solution.“DigRF requires just 10 external componentsto implement a complete RF section with adigital interface,” said the Woburn, MA, firm.

Meanwhile, RFMD has extended its pene-tration into Motorola’s existing EDGE hand-

set portfolio with a deal to supply its Polaris 2Total Radio chipsets into the V360 phone.

Endwave unveils rights plan as shares sink

TriQuint Semiconductor is to usespecialty electronics distribution company RFMW to distribute its productsin North and South America. RFMWworks exclusively on RF and microwaveproducts, and offers componentengineering support. Raytheon says that its APG-79 next-generation radar, which features III-Vcomponents, has enabled military aircraft

to fire high-precision missiles at multipleattack targets simultaneously – somethingthat the company says has not beenpossible before. Wicht Technology Consulting inGermany says that the market for all typesof RF MEMS components is set to rocketfrom just $126 million in 2004 to over$1.1 billion by 2009. Cell phones willprovide the largest sector, it adds.

In brief

RFMD’s Polaris 2 Total Radio chipset will be used in Motorola’s V360 EDGE handset.

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GAAS & WIRELESS NEWScompoundsemiconductor.net

Japanese supplier Hitachi Cable topped arecent study that rated the different vendorsof semi-insulating (SI) GaAs bulk substrates.

According to Strategy Analytics, whichconducted the poll, Hitachi beat FreibergerCompound Materials (FCM) and SumitomoElectric Industries (SEI) into second and thirdplace respectively, with AXT and DowaMining rated in fourth place jointly.

“FCM, Hitachi Cable and SEI achieved thehighest ratings for both technical and com-mercial parameters,” said Strategy Analytics.While there was no discernible difference inthe technical ratings achieved by the top three,the survey also took into account factors suchas wafer pricing, wafer uniformity and lot uni-formity among ten different parameters.

According to Strategy Analytics, SEI’srating was affected by the company’s ten-

dency to keep its primary customers happy atthe expense of smaller ones.

In a similar survey of SI epiwafer suppli-ers, Strategy Analytics concluded that sup-pliers from the non-Japan countries of theAsia-Pacific region rated highly because oftheir low wafer prices.

Singapore-based MBE Technology wasawarded the top spot in the epiwafer suppliersurvey, with strong showings on price andother commercial parameters and “reason-able” scores on technical requirements.

“Despite some exceptional scores in certaincategories, the overall performance of epi-wafer suppliers has been poor when judgedalongside end-user expectations,” found thesurvey. “The industry delivered on flatness andtest data in 2004, but these parameters werelow on the list of priorities for the end-user.”

With its eye on the automotive telematicsmarket, US-based RFIC manufacturerAnadigics has introduced a new additionto its family of RF switches.

As a 10W-rated PHEMT antennaswitch, the AWS5532 can also be used inGSM, CDMA and WLAN mobile platforms.“The adoption of telematics in theautomotive industry offers users manynew services, including remotediagnostics, on-demand navigation, andfleet tracking,” said Ali Khatibzadeh, whoheads up the wireless products division atAnadigics’ Warren, NJ, headquarters.

RF Micro Devices (RFMD) has qualified alaser dicing tool in full production at one ofits GaAs fabrication facilities.

The Greensboro, NC, company, whichholds an estimated 44% share of the poweramplifier (PA) market, is one of the biggestGaAs chip manufacturers in the world, and isthe first to use a fully automated laser dicer.

Supplied by the Swiss company Synova,the system is unique in that it features a waterjet to both guide the laser beam and cool thesemiconductor wafer surface (see CompoundSemiconductor June p29).

First used in medical applications, theSynova tool has since been employed for sili-

con wafer processing. However, developingthe system to dice GaAs wafers has provedmore problematic because of the toxicity ofgallium and arsenic, which can be releasedduring the laser-dicing process.

Synova claims that wafer damage and toxiccontamination cannot be avoided with con-ventional “dry” laser dicing, although suchsystems have been trialled by GaAs chipmanufacturers.

In the latest installation at RFMD, 100 µm-thick GaAs wafers have been diced to give a23 µm kerf. According to Synova, through-cutting was achieved in a single pass of thelaser beam at a speed of 50 mm/s.

RFMD employs laser dicer at GaAs fab

Hitachi Cable voted bestSI GaAs substrate vendor

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LED NEWS compoundsemiconductor.net

COMPOUND SEMICONDUCTOR DECEMBER 20058

Holographic photonic crystalsincrease extraction efficiency

Japanese chemicals company Showa Denko(SDK) has earmarked ultra-bright LEDs asa key part of its new business strategy, whichit calls the Passion Project.

The company is better known in the widersemiconductor community for its high-purityammonia products, used in etching applica-tions, where it claims to have a 30% marketshare. In the past it has also developed 6 inchInPsemi-insulating wafers and manufacturedInGaP HBT epiwafers.

More recently the company began pro-ducing compound semiconductor devices,and in November SDK revealed plans to makehigh-brightness green and ultraviolet LEDsin large volumes.

In its latest business plan, SDK has iden-tified ultra-bright LEDs as one of five impor-

tant product areas to be developed at “anaccelerated pace”.

The company expects to see growth inapplications such as LCD backlighting, carheadlamps and general lighting. “We aim to[make] ¥20 billion ($167 million) in ultra-bright LED sales in 2008,” SDK predicted.

Across the five businesses identified asgrowth areas, SDK has said that it will invest¥200 billion over the next three years. Assu-ming that even a small share of this total is allo-cated for the development of its LED business,that still equates to an investment of severaltens of millions of US dollars in compoundsemiconductors.

SDK also plans to grow its semiconductormaterials business, aiming to almost doublesales to ¥30 billion by 2008.

Rajiv K.Agarwal,Ph.D.LeadResearchEngineer

Higher background levels ofn type dopants in GaAs andAlGaAs structures are causedby trace levels of germanium,

silicone and sulfur species present in the arsine.As customer applications evolve, the purityrequirements for arsine must as well. Untilrecently, background doping levels of 1015/cm3

were considered acceptable in most applica-tions. In general, most currently available high-purity grades of arsine can satisfy these require-ments. However, process changes and demandfor more sophisticated devices have resultedin the need for lower background doping levels.To address these more stringent requirements,Air Products is introducing MegabitTM IIIarsine, our purest grade available. Our newMegabit III arsine has significantly reduced theamounts of germanium, silicon and sulfur spe-cies. Testing done at an independent laboratoryproved the effectiveness of Megabit III on thickgallium arsenide films, with excellent results.In all cases, the background doping level was<<1014/cm3. Our research has shown thatAir Products’ Megabit III arsine will performmore consistently and produce fewer defectsin our customers’ finished products.

For more information or to submit aquestion for "Ask the Expert," visit us atwww.airproducts.com/AsktheExpert or callus at (800) 654-4567 or (610) 706-4730 andmention code #144.

© Air Products and Chemicals, Inc., 2004 (24061) LCS-1

tell me morewww.airproducts.com/AsktheExpert

Ask the Expert

I am experiencing highn type backgrounddoping levels in myMOCVD process when Igrow GaAs and AlGaAsdevices. I think theproblem is in the arsineI use. I’m buying the bestgrade available. Whatcan I do?

A

Q

Showa Denko develops apassion for bright LEDs

By James TyrrellKorean scientists have more than doubled theoutput power of GaN-based LEDs thanks toa holographic process that etches a two-dimensional photonic crystal (PC) into thedevice. The researchers say that their holo-graphic method is a major improvement onprevious work using electron-beam litho-graphy, as the technique suits large-area pro-cessing with high throughput (Appl. Phys.Lett. 87 203508).

Typically, a large portion of the light gen-erated by an LED is wasted because of inter-nal reflection and lateral waveguiding. Byintegrating a PC lattice within the device struc-ture, LED makers have the opportunity to con-trol photonic behaviour and improve lightoutput. Researchers from Seoul National Uni-versity used a two-beam holography set-upequipped with a He-Cd laser (325nm) to writesquare-lattice PC patterns with periods of300 nm, 500 nm and 700 nm. LED waferswere provided by Samsung’s Advanced Ins-titute of Technology.

The team found that its 500 nm latticeoffered the best performance, with the deviceextracting 2.1 times more light than a con-ventional planar LED. “The only problem we

noticed was a slight increase in operating volt-age, but this can be solved in the future,” saidHeonsu Jeon of Seoul National University.

Jeon thinks that the addition of a photoniccrystal pattern should not cause any signifi-cant increase in the cost of the LED. “In thefuture, the laser holography method could[even] be replaced with a phase mask tech-nique to suit a mass production environment.”

James Tyrrell is a reporter for Optics.org andOpto & Laser Europe magazine.

The LEDs containing photonic crystals with periods of 300nm (b), 500nm (c) and700nm (d) deliver a significantly higheroutput than the reference planar LED (a).

a b

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9COMPOUND SEMICONDUCTOR DECEMBER 2005

LED NEWScompoundsemiconductor.net

HB-LED suppliers top100More than 100 companies now produce high-brightness (HB) LEDs at various levels of thevertical supply chain. That’s according to thelatest analysis of the industry by the marketresearch firm Strategies Unlimited.

While the $3.7 billion market for packagedHB-LEDs in 2004 was dominated by just ahandful of key suppliers, the report indicatesthat there is still room for new companies tofill niches with either novel device packagingor innovative chip structures.

Bob Steele, the analyst company’s direc-tor of optoelectronics programs, says that outof the 30 companies selling epitaxial wafersand/or HB-LED chips into the market in 2004,the top three suppliers accounted for over halfof the sales of these materials.

Steele adds that the HB-LED industry isyet to become highly integrated. Out of the 74companies analyzed, only 12 are verticallyintegrated from epiwafers and chip produc-tion through to the packaging stage.

And while 26 of the companies profiled inthe report produce only epiwafers or chips,this does not represent the biggest single group– 36 firms purchase chips and produce pack-aged HB-LEDs.

Asia still dominates in terms of production,accounting for 76% of the packaged HB-LEDmarket and 57% of merchant epiwafer andchip sales in 2004.

“In spite of some industry consolidation,we can expect to see new HB-LED supplierscontinue to enter the market,”said Steele.

Researchers from Meijo University, Japan,report that they have doubled the efficiencyof white-emitting LEDs by producing a devicethat delivers 130 lm/W, according to theJapanese web-site Nikkei.net.

Team member Satoshi Kamiyama toldCompound Semiconductor that the increasedoutput was produced by employing a purple-emitting GaInN-based multiple quantum wellfor the active region and using impurities in

the SiC substrate for white light conversion.This approach contrasts that taken by many

LED makers, who use blue-emitting devicesand color-converting yellow phosphors.

Kamiyama has also secured ¥40 million($330,000) to launch a company that willdevelop the GaInN-based LEDs. The cashwill be spent on marketing the devices and onwinning an additional ¥30 billion, whichcould be used to build a chip production line.

Substrate impurities boost white output

Mistrust between manufacturers of high-brightness (HB) LEDs and their customers isjust one of several issues that the solid-statelighting (SSL) industry must address if it isgoing to succeed.

That’s one of the findings of an analysis ofthe global market for HB-LEDs compiled byNanoMarkets, an offshoot of Communica-tions Industry Researchers.

NanoMarkets predicts rapid growth in themarket for LEDs in general, and for the

highest-brightness devices in particular. However, the analyst company also says

that the industry must address a range of prob-lems for SSLto penetrate mainstream lightingapplications. These include more transparencyand co-operation between different levels ofthe industry supply chain, a greater marketingemphasis on the consumer benefits of LEDs,and new characterization standards. Read more details about the NanoMarketsreport on p19 of this issue.

Industry in need of uniform standards

KoBrite, the joint-venture company setup by Kopin to mass-produce LED chips,has officially opened its Chinese facilities.The new three-building campus inDongguan, near Hong Kong, will hostGaN-based LED die processing activity,with epitaxy taking place in Taiwan.

Osram says that improvements to thestructure of its TOPLED range of powerLED chips will enable the products to beused in applications that up until now havebeen dominated by traditional light sources.The advancement is said to produce50–70% brighter AlInGaP devices.

In brief

Long-lasting, reliable lighting. Accessible in themost inaccessible locations imaginable. That’s the promise of LEDs. And thanks to NuSil, high-powered versions will soon be available fromKaohsiung to Cape Canaveral to Kodiak, Alaska.

While our advanced packaging materials are helpinghigh-brightness LEDs fulfill their potential, yourneeds might be very different. From LEDs to fiberoptics, large batches to small, our Lightspan brandof products deliver precise, custom formulationsand the most complete line of high-refractive indexmatching adhesives, encapsulants and thermosetsavailable. All backed by more than 25 years ofengineering materials expertise.

What? When? Where? If it’s NuSil, it’s no problem.

Miles from civilization.

Can’t see a thing.

Light up the night.

NuSil Technology.

What’s your challenge? www.nusil.com or 805/684-8780

©2005 NuSil Corporation. All rights reserved. CS0205-PH

OPTO NEWS compoundsemiconductor.net

COMPOUND SEMICONDUCTOR DECEMBER 2005 11

Brighter LEDs speed up water purification

Materials, component and optical system sup-plier Emcore has acquired the California-basedfirm Phasebridge, which produces fiber-opticgyroscopes (FOGs) used in applications suchas weapons and aerospace guidance.

The FOGs made by Phasebridge are basedaround a superluminescent LED chip manu-factured on InP.

Phasebridge also makes multichip opticalmodules for applications such as RF deliveryover optical fiber links, RF frequency syn-thesis and terahertz spectroscopy.

The Pasadena-based firm will be integratedinto Emcore’s Ortel division, which was for-merly part of the Agere Systems optoelectron-ics business and is based close to Phasebridgein Alhambra, CA.

“Ortel will [now] be able to offer a broad setof component and subsystem solutions in the

FOG, RF, microwave and terahertz marketsfor a range of applications,” said Hong Hou,Ortel’s vice-president and general manager.

Earlier this year Phasebridge introduceda prototype three-axis FOG transceiver that itdeveloped for the US Navy.The transceiverwas said to be the first in the industry to inte-grate all three axes into a single package.

Emcore buys gyroscopespecialist Phasebridge

Emcore can now offer three-axis fiber-opticgyroscope transceivers from Phasebridge.

Hydro-Photon, a developer of UV LED-basedwater treatment modules, has purified waterat flow rates close to those required for indi-vidual water treatment systems.

Miles Maiden has increased flow rates thisyear by replacing existing UV LEDs withmore powerful versions made by RemisGaska’s team at Sensor Electronic Technol-ogy and Asif Khan’s group at the Universityof South Carolina.

Hydro-Photon’s treatment chamber cannow reduce the level of E. coli-spiked waterflowing at 150 ml/min and 300 ml/min by99.99% and 99%, respectively. The figures

are close to the values required for individualsystems, which would typically work at a flowrate of at least 500 ml/min.

The latest work is also an improvement onthe 38 ml/min rate for a 99.99% reduction ofE. coli that was achieved earlier this year (seeCompound Semiconductor May p15).

The latest LEDs used in the modules delivera UV output of 7.34 mW, compared with2.6 mW for the previous generation of emit-ters. The wall-plug efficiency of the UV LEDshas also risen from 0.63% to 1.52%, while theaverage forward voltage has reduced from6.6 V at 65 mA to 5.9 V at 83 mA.

Phone: +49 9665 9140-0Fax: +49 96651720info@linn.de

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Bridgeman 3 zone vertical tubular furnacewith graphite heater for directional /and single crystal solidification ofmetals under protective gas atmos-phere. With quenching buffle. High precisiontranslation. Program controller: SE 502.Max. furnace temperature: 1.800 °C. Max. hea-ting power: appr. 20 kW. Linear unit: 0,1 mm/hto 1.000 mm/h. Fast cooling: appr. 100 mm/s.

GaIn

Micro-Crystal growth systemfor pulling of single crystalline fibers from the melt under inert gas or air. Fiberdimensions: Ø = 0,2-2,0 mm, lmax = 250 mm.Up to 5000 mg of starting material is melted in aplatinum crucible (for high-melting compoundsalso Ir-, W-, Mo- crucibles) and a fiber crystal ispulled down through a capillary nozzle with asecondary heater around the nozzle. Powersupply: primary heater 80 W (max. 500 W),secondary heater 30 W (max. 200 W).

LiNbO3

Production system for sublimation growth of 2 / 3 inch 4H- and 6H SiC single crystals for optoelectronics, power- and high temperature electronics. Allowsthe precise control of process conditions (tempe-rature field, gas pressure, gas composition).

Tmax 2300 °C.

SiC

The Semiconductor Industry Association(SIA) has forecast that the global opto-electronics market will grow by around10% each year and be worth almost$21 billion in 2008.

The prediction was part of the SIA’swider forecast for the entire semiconductormarket, which it believes will surpass$300 billion in three years’ time. SIAvalued the overall market at $213 billionfor 2004, adding that the optoelectronicssector was worth $13.7 billion.

Film maker Metro-Goldwyn-Mayer(MGM) says that it plans to release filmand television titles from its library in Blu-ray format when the associatedhardware is launched in North America,Japan, and Europe.

“Blu-ray technology, with its expandedstorage capacity and increased interactivecapabilities, allows us to continue toprovide our customers with the best movieexperience available,” said Harry Sloan,CEO of MGM Studios.

In brief

EM

CO

RE

Firecomms, an Ireland-based developer ofhigh-speed semiconductor light sources, saysthat it has unveiled the world’s first mediaorientated system transport (MOST) fiber-optic transceiver based on a high-speed reson-ant cavity LED (RCLED).

MOST networks are plastic optical fiber-based infrastructures deployed in cars to linkvarious electronic systems, offering a low-cost alternative to copper cabling.

Firecomms’ transmitter uses an RCLED– a device that is similar to a VCSEL butwhich has a much larger aperture and does notlase. The RCLED is integrated with a lens to

maximize coupling efficiency.Firecomms’ RCLED technology “offers

improved device efficiency, high bandwidth(to 250 Mb/s), and excellent reliability”, saidCTO John Lambkin.

“Because our core light sources are signifi-

cantly faster than existing fiber-optic trans-ceivers, we can provide our customers withthe ability to migrate to next-generation sys-tems while maintaining existing connectorsand a plastic optical fiber architecture,” addedthe company’s CEO Declan O’Mahoney.

FIBER NEWS compoundsemiconductor.net

COMPOUND SEMICONDUCTOR DECEMBER 2005 13

Firecomms revealsRCLED transceiver for in-car networks

The global market for optical equipment usedin communications systems has grown by31% in the past year, claims a new report byanalysts at Dell’Oro Group.

Alcatel ranked highest of the system ven-dors, sharing a worldwide market worth$2.1 billion in the third quarter of 2005. TheFrance-based company was followed byNortel, Lucent and the Chinese firm Huawei.

“The optical market continues to exceedmy expectations,” said Jimmy Yu, Dell’Oro’sdirector for optical transport research. “Thiswas the fourth consecutive quarter of higheroptical revenue in North America, keeping theworldwide optical market in a state of growth.”

Long-haul applications are showing par-ticularly strong growth in North America, andin the specific area of 10 Gb/s systems, pho-tonic integration specialist Infinera appearsto be stealing market share away from its moreestablished rivals.

The company, which manufactures mas-sively integrated chips at its own InP fabrica-tion facility in Sunnyvale, CA, says that itranked number one in Dell’Oro’s latest sur-vey of high-speed, long-haul optical networksystem suppliers.

“We are thrilled to rank first in the Dell’Orofigures only 10 months after we began ship-ping our product,” said Jagdeep Singh, the co-

founder and CEO of Infinera.The company has revealed details of five

customers since it began officially shippingproducts in late 2004. Measured in terms ofthe number of 10 Gb/s wavelengths shippedin the third quarter, Infinera took a marketshare of 20%.

Infinera’s photonic integrated circuitsfeature more than 60 optical components on asingle chip, and are manufactured usingMOCVD. The firm now deploys 100Gb/s sys-tems and is also planning to roll out 400 Gb/sversions over the medium term, believing thatthe data rate demanded by network operatorswill double every two years.

Optical CommunicationProducts (OCP), which makesfiber-optic subsystems andmodules out of its WoodlandHills, CA, base, posted arevenue of $14.8 million in itsfinal quarter of fiscal 2005,which ended on September 30.

The sales figure representeda sequential increase of 8.7%and was 12.5% higher than theequivalent period last year,highlighting what the firm’sCEO, Muoi Van Tran,described as a “higher level

of activity” from customers. A new InP foundry service hasbeen launched. Svedice, a firmwith 14 employees based inJärfälla, Sweden, has customersthroughout the world and isequipped with a 800 m2

cleanroom and facilities thatinclude MOCVD growth,materials characterization,etching and metallization.

The start-up can produce1310 nm and 1550 nm fixed-wavelength and tunable lasers,and standard and avalanche

photodetectors for 2.5 Gb/s and10 Gb/s applications. Finisar posted sales of$86.6 million, up 6%sequentially and an increase of 22% year on year, for thesecond fiscal quarter endedOctober 31. Loss for the quarterwas $15.8 million.

In the current quarter thecompany has bought the opticaltransponder assets of Big BearNetworks for $1.9 million incash. “The acquisition expandsour 10 Gb/s product offerings

and adds new 40 Gb/stransponders to our productline,” said CEO Jerry Rawls. JDSU has acquired tunablelaser manufacturer AgilityCommunications for$67 million.The transactioncomprised $57 million in stockand $10 million in cash.

The firm has also gained theapproval of its shareholders toimplement a reverse stock splitin the range one-for-eight toone-for-ten at any time beforeDecember 1, 2006.

In brief

Infinera gains as long haul improves

Firecomms hopes that car makers will turn to RCLED-based communications networks.

The fablessapproach hasdoubtless beena major reasonwhy Hittite hasbeen profitablein each of its last13 years ofoperations.

If you invested in Hittite Microwave’s initial publicoffering (IPO) back in the summer, then you will havealready made a tidy profit for the approaching holidayseason. But is it wiser to hold onto those shares, or tocash in the return at such an early stage?

Since late July, when the ticker name “HITT” madeits debut, the stock price has enjoyed a steady climbfrom the IPO valuation of $17 per share, easily outper-forming the Nasdaq composite and just topping $25in mid-November as Compound Semiconductor wentto press. Clearly, investors have been convinced by theChelmsford, MA, company.

Massachusetts Institute of Technology (MIT) gradu-ate Yalcin Ayasli, who founded Hittite back in 1985, sawa major return on his own investment through the IPO,which boosted the balance sheet by around $52 million.With more than 16 million shares in the company, theAyasli family’s holding in Hittite now has a value inexcess of $400 million.

The name “Hittite”– a reference to an ancient peo-ple living in northern Syria some 4000 years ago – giveslittle clue as to the nature of the company’s business. Infact, the secret of its success appears to owe much to theselection of a fabless business model to manufactureRFICs, modules and subsystems. Hittite uses seven dif-ferent foundries to make its chips, which range fromadvanced silicon devices such as SiGe and silicon-on-insulator components to GaAs-based power amplifiers.

The fabless approach has doubtless been a major rea-son why Hittite has been profitable in each of its last 13years of operations. And in its third quarter of fiscal 2005,which ended on September 30 (the second set of resultsto be announced since the company’s IPO), Hittite’s

profit margin looked particularly healthy. Overall rev-enue was only $21.2million, just one-tenth that of GaAschip manufacturer Skyworks Solutions, for example.But on the bottom line Hittite posted an impressiveprofit of $5 million, equivalent to $0.17 per share, com-pared with Skyworks’$3 million ($0.04 per share).

As well as registering an impressive year-on-yearrevenue increase of 32.5%, Hittite is looking to expandits range of customers. In the most recent quarter, 57%of the company’s revenue came from US sales, with themilitary, microwave and millimeter-wave communica-tions, and broadband segments accounting for 70% ofrevenue. Increased sales into cell-phone, automotive andspace applications are among the targets for the future.While Hittite CEO Steve Daly acknowledges that salesto cellular applications have softened slightly in recentmonths, specifically in Asia, he believes this to be a tem-porary slowdown, with the ramp of 3G communicationsglobally providing very strong activity in general.

As well as generating $6.4 million in cash from con-tinuing operations in the September quarter, Hittite hasalso been busy on the acquisition front. In late Augustthe company acquired Q-Dot, a research and develop-ment organization that specializes in designing mixed-signal silicon ICs, for $2.2 million in cash. TraditionallyQ-Dot has, like Hittite, been focused mainly on mili-tary applications for the US Department of Defense,with whom it has an existing backlog of projects worth$3 million. However, the intention in the future is tobroaden this applications base by targeting the com-mercial markets that Hittite has already penetrated.

Because of its fabless business model, Hittite isexposed to market forces resulting from fluctuations inthe semiconductor foundries that it uses. With the boom-ing cell-phone handset industry, many of these GaAsfabs, which include the pure-play foundry GlobalCommunication Semiconductors, as well as TriQuint,M/A-COM and United Monolithic Semiconductors,have seen utilization rates grow in recent months.

However, Daly says that this trend is not adverselyaffecting Hittite because the fabs are still running ataround 50% capacity, which is not high enough to affectwafer prices or lead times.

Looking forward, Hittite’s management has alsoraised its guidance for the final quarter of the calendaryear on the back of a better-than-expected gross mar-gin, with revenue expected to be in the $22million rangeand net profit of $5.4 million–$5.7 million.

With its impressive financial history and solid out-look, it would seem that Hittite shares are worth hold-ing onto well beyond this holiday period.

Since its Nasdaq debut in August, Hittite Microwave’s stock has already provided shareholders witha valuable return on investment. Michael Hatcher tracks the fabless IC company’s recent moves.

Hittite proves fabless benefits

www.compoundsemiconductor.netPORTFOLIO

COMPOUND SEMICONDUCTOR DECEMBER 200514

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Convincing: Hittite has outperformed the Nasdaq average since its July 2005debut at $17 per share, with a 46% increase in the stock’s value by December.

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COMPOUND SEMICONDUCTOR DECEMBER 200516

Ask any incumbent telecom company to con-nect two individual gigabit-per-second local-area networks (LANs) and you will be offered1,000 DSLlines, 647 T1 lines or 500 E1 lines.The copper plant that links users to the com-munications backbone was never designed toconnect modern computers. Gigabit capacityexists in the fiber rings, the LANs, and thecomputers, but just a few thousandths of thisspeed is available in the local copper loop.

Fiber can be installed in the last mile, butthis occurs infrequently. The 7,500 nationaland international long-haul fiber rings and the100,000 local metropolitan rings deployedworldwide have only a few fiber-optic “lat-erals” connecting them to individual build-ings. US businesses use Ethernet networksthat operate at 1 Gb/s and computers that runat even higher data rates, and yet 95% of themhave no fiber connection.

The lack of provision of fiber services tomost buildings arises from the high cost oftrenching ($0.2–$0.8 million/km in urbanareas), and the 6–12 month wait for installa-tion (caused by the time taken to gain accessto private land). The process of laying under-ground cables has failed to keep pace with theadvances in telecommunications and com-puting. For this reason a market exists for alower-cost, millimeter-wave radio solution.Radio links can fulfill the demand for high-speed connections from premises to wide-areanetworks. In the US, 750,000 business loca-tions could benefit from a radio link.

The aerial routeMillimeter-wave radio offering gigabit-per-second data rates can be deployed within a fewdays, and for a fraction of the trenching costs.These millimeter-wave high-data-rate radiosusually cover a 1.6 km range. Although tor-rential rainfall can impede the propagation ofthese signals (see “When the rain comesdown”, p17), the technology can usually pro-

vide connectivity for all but five minutes peryear. If customers are prepared to accept thisvery infrequent disruption, gigabit-per-secondradio can serve the 80% of US businesses thatare located within 1.5 km of a fiber network.

Today’s microwave radios are limited bycost to 100–200 Mb/s data rates, predomin-antly because the regulatory agencies haveauthorized only narrow bands. However,because these rates are insufficient for today’sneeds, GigaBeam has worked with the FederalCommunications Commission (FCC) to cre-ate rules and authorize the use of spectrum at71–76GHz, 81–86GHz, and 92–95GHz. Theuse of these bands was approved in October2003, and since then GigaBeam has cham-pioned the adoption of similar legislation withregulatory agencies throughout the world.

The spectral bands centered at 73.5GHz and

83.5 GHz are each 5 GHz wide. If low-ordermodulation formats delivering 1–3 bits/Hzare used, a low-cost 1–10 Gb/s transmissiontechnology is viable. Although the 92–95GHzspectrum has a 100 MHz band reserved forspace-borne radios right in the middle of theband that limits transmission to a few giga-bits, this data rate is still valued for next-generation networks.

In commercial environments cost domin-ates the decision-making process. In general,if you want a lower cost you turn to silicon.Intel has built silicon circuits that operate at100 GHz, while IBM has used SiGe circuitsto produce similarly impressive results. How-ever, practical, longer-range radios cannot be built with silicon-based components, soGigaBeam has chosen GaAs MMICs for itstransmitters. We have found that existing

COVER STORY

The cost of deploying fiber to the premise limits the data rates available to most US businesses. The solution, say Doug Lockie and Don Peck of GigaBeam, is to connect fiber networks toenterprises by millimeter-wave radio transmissions, delivering gigabit-per-second data rates.

BROADBAND WIRELESS

GigaBeam has deployed its high-speed radio transmitter at Trump Towers, New York City,where residents have the luxury of receiving fiber-equivalent access in their own apartment.

GigaBeam turns to III-Vs forultra-fast broadband radio

17COMPOUND SEMICONDUCTOR DECEMBER 2005

COVER STORYcompoundsemiconductor.net

GaAs MMICs produced by Velocium, a com-mercial semiconductor division of NorthropGrumman, have produced excellent resultsat our frequency range.

The subsystems that form the millimeter-wave circuits include receivers, converters,transmitters, oscillators and modulators/demodulators (modems). The nominal per-formance parameters required by these parts

are outlined in “Requirements for radio sub-system components” (p18).

Among all of the performance parametersof millimeter-wave circuits, one that rarelyreceives sufficient attention despite its highimportance for communication applicationsis the temperature dependence of the gain perstage. Each stage has a thermally induced gainvariation of 0.1dB per 10°C that depends only

slightly on the actual gain of the stage.A typical radio requires 60 dB gain to both

transmit and receive signals, and must operateover a 100 °C temperature range. Since everygain stage contributes 1 dB of gain variationover the temperature range, the key parameterfor radio applications is a high gain per stage.

GigaBeam has found that the GaAs circuitsdeliver sufficient gain per stage, unlike their

BROADBAND WIRELESS

The weather strongly influencesmillimeter-wave propagationand limits connectivity (figure 1).The proportion of time whencommunication is lost becauseof bad weather is defined interms of “nines”. Five nines is a maximum downtime of fiveminutes per year (99.999%availability), four nines is lessthan 50 minutes withoutconnectivity per year (99.99%availability), and so on.

At the frequencies used byGigaBeam, rain producesgreater signal attenuation thanfog or atmospheric gases.However, a rainfall rate of150 mm per hour occurs for less than five minutes each year(“five nines”) across about 80% of continental US and 90% of Europe.

In the past, radiocommunication operated at

frequencies that were largelyunaffected by rainfall, andengineers used a rule of thumbthat stated that increasing thelink system gain by 4 dBdoubled the range. Millimeter-wave applications, however, aresignificantly different.

The rule of thumb can beapplied to millimeter-wavecommunication in clear air, butpropagation through heavy rainthat corresponds to a “five nineslevel” availability needs a further50 dB of gain per mile toovercome the additionalattenuation. With today’stechnology, the weather limitscost-effective, practical,millimeter-wave gigabit-per-second links offering “five nines”availability to a range of 1.6 km.

So, for a 1-mile link using50 dB gain antennas that are typically 0.6 m high, just

1 µW of power is required fortransmission in clear air at1.25 Gb/s using biphase shiftkeying modulation, assuming a–60 dBm threshold for 2.5 GHz

radio-frequency bandwidth.However, in adverse weatherconditions nearly 0.4 W can beneeded to deliver the samesignal level (figure 2).

When the rain comes down

millimeter

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2 miles1 mile

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0.4 W

0.1 W

40 kW

(a)

(b)

(c)

Fig. 1. When operating in the 71–95GHz spectral range, rainfall andatmospheric gases can have a strong effect on signal propagation.

Fig. 2. (a) In clear air a transmitter emitting just 1µW is sufficient to cover a 1mile radius. To transmit to 2miles, 4µW would berequired if the second mile was also in clear air. (b) With intenserainfall delivering “five nines” attenuation in the first mile, thetransmitter’s power needs to increase to 0.1W for a 1mile radius,and to 0.4W for 2miles. (c) If rainfall occurred over both miles, a40kW transmitter would be needed for the second mile. Thisoutput power is not possible, so GigaBeam’s radio range offering“five nines” availability is restricted to 1 mile. However, if thecustomer accepts “four nines” coverage, a 2mile range is possible.

COVER STORY compoundsemiconductor.net

COMPOUND SEMICONDUCTOR DECEMBER 200518

silicon-based counterparts. Velocium’s GaAschips produce a total of a 10 dB variation, solittle additional circuitry is required to com-pensate or deliver additional gain. However,silicon circuits producing a 20 dB gain vari-ation require four to six additional gain stagesto overcome the losses, as well as a similarnumber of circuits that typically use PiN diodeactuators for gain compensation.

High data rates with InPGigaBeam recently signed an exclusive agree-ment with Vitesse Semiconductor to use itsVIP II HBT technology base for radio appli-

cations from 50 GHz to 300 GHz. Vitesse waschosen because its InPmanufacturing processcan produce transistors with ft and fmax valuesof 400GHz and 450GHz, respectively, as wellas deliver high yields for digital circuitry withseveral thousand gate equivalents. To the bestof our knowledge this is the only manufac-turing process that produces this number ofgates with a high yield on InP, and we believethat it has the potential to deliver high-speedanalog-to-digital converters.

GigaBeam will use these circuits for sev-eral signal processing functions within theradio, and our main goal is to develop a 4–6bit

A/D converter with a 90 GHz sampling rate.If successful, this A/D converter will enablea new generation of demodulators for 10 or20 Gb/s links. The target is higher perfor-mance and lower cost for the advanced tech-nology base. The first 10 Gb/s radio willprobably deploy an analog architecture andoperate at 3bits/Hz, and make use of the entire5 GHz band. Looking further ahead, evenfaster data rates are possible by using higher-order modulation schemes featuring 64 or 128quadrature amplitude modulation processesand a digital architecture.

This year GigaBeam’s radio transmittershave enabled the company to win contractsfor installation in various locations, includingDartmouth College, Boston University, andthe Trump Building in New York City. Thedevelopment of radio transmitters featuringeven faster data rates will only help to gen-erate additional business.

Doug Lockie is GigaBeam’s president andCTO (doug.lockie@gigabeam.com), and DonPeck is GigaBeam’s vice-president ofengineering (don.peck@gigabeam.com).

BROADBAND WIRELESS

Receiver Gain of 15–25 dB, noise figure of 2–5 dB.Transmitter Gain of 10–40 dB, power output (1 dB) 20–25 dBm. The FCC limits power

output to 3 W, and it is desirable to produce this power if it is cost effective.Oscillator Phase noise of –100 dBc-Hz at 1 MHz offset for a 40 GHz center frequency.

The active device contributes to this specification, but a “high Q” network isthe primary driver.

Converter Nominal 12–15 dB conversion loss.IF strip 3–20 GHz (usually silicon), 30–70 dB of gain.Modem 1–10 Gb/s at 3–15 GHz IF center (usually silicon).

Requirements for radio subsystem components

MARKET REPORT compoundsemiconductor.net

COMPOUND SEMICONDUCTOR DECEMBER 2005 19

Industry must work togetherto displace light bulb culture

The penetration of high-brightness (HB)LEDs into the general lighting market seemscloser to becoming a reality as manufacturerslook to extend their applications base beyondcash cows like the mobile phone.

Improvements in LED chip structures andpackaging will of course be fundamental tothis switch, but technology alone will not beenough to create a solid-state lighting (SSL)market. According to some commentators, theHB-LED industry needs to change some of itsways to make this happen.

One of those commentators is the analystfirm NanoMarkets, which has just released itssecond market report on the HB-LED busi-ness. As well as providing the usual estimateof the size of the sector and its potential forgrowth, Rob Nolan and Lawrence Gasmanfrom NanoMarkets have identified severalproblem areas that they believe the industryneeds to address to keep growing strongly.

They value the HB-LED market (definedas packaged sources emitting 50–250 lm) at$4.1 billion in 2005, and Gasman predictssteady if unspectacular growth over the nexteight years as existing application areasincrease in size. During that time there shouldbe much faster growth in the “ultra-high-brightness” area, as HB-LEDs gain a footholdin more demanding applications such as auto-mobile headlamps and general lighting.

RelationshipsBut the message from Gasman and others isthat just relying on the technological superior-ity of HB-LEDs over conventional sources willnot be enough to effect the latter’s replacement.

“Compact fluorescent lamps had [techno-logical] advantages over incandescent lamps,but the industry did a poor job of selling thattechnology and it didn’t take off,” said Gasmanof one recent attempt to take on the light bulb.While he believes that the HB-LED industrycan do a better job, there remain plenty ofissues that need to be addressed along the way.

One of these relates to the sometimes thornyrelationship between HB-LED suppliers and

the lighting equipment makers that use thechips in their products. “There is a level ofmistrust,” Gasman said, although this is notsurprising in what is still a relatively youngindustry where technology is a key differen-tiator. “The lack of a consolidated effort by HB-LED manufacturers with OEMs has beena hallmark and a drawback for the HB-LEDindustry,” states the NanoMarkets report. Itadds that chip manufacturers are too con-cerned about their patented chip designs beingcopied and made into cheaper products.

More important in the years to come, how-ever, will be the relationships between chipmanufacturers and their customers. In timethese relationships will become just as valu-able in terms of competitive advantage astechnology patents are today.

With Philips now in complete control ofLumileds Lighting, things may start to changemore quickly. This is a step that Gasmanbelieves will be replicated by more big play-ers in the lighting industry, although withGeneral Electric’s stake in GELcore andOsram’s Opto Semiconductor LED sub-

sidiary, it could be argued that the biggestplayers have already made this move.

Another analyst firm, Strategies Unlimited,has also been looking at the degree of verticalintegration within the HB-LED business. Ithas just published the results of its latest indus-try survey, finding that over 100 companiesare now involved in the supply of either HB-LED epiwafers, dice or packaged devices. Ofthose, 12 are described as vertically integrated.

Not everybody believes that a large degreeof vertical integration is the best way forwardfor the industry, however. For example, at therecent LEDs 2005 conference in San Diego,Makarand Chipalkatti – the head of corporateinnovation management at Osram’s Sylvanialighting business – argued against the idea.But he agrees that to challenge the light bulbculture HB-LED makers must become lessobsessed by technology and increase collab-oration to address issues of industry infra-structure, which he now sees as a priority. “It’stime to move to the next step,” he told dele-gates, urging them to work within industrygroups to mount an effective challenge that

HB-LED manufacturers should concentrate on building relationships with their customers in orderto break down the incumbent culture based around the Edison light bulb, say analysts.

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s)ultra HB-LEDs >250 ImHB-LEDs (50–250 Im)standard LEDs 5–50 Imindicator LEDs <5 Im

LED market growth according to analyst firm Nanomarkets. The eight-year forecastpredicts a massive increase for “ultra-high-brightness” LEDs (packages emitting morethan 250 lm). If automotive headlamp and general lighting applications kick in as theanalysts predict, this particular sector could be worth an astonishing $7.6billion by 2013.

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21COMPOUND SEMICONDUCTOR DECEMBER 2005

MARKET REPORTcompoundsemiconductor.net

he regards as the biggest change in lightingfor nearly a century.

But while the incumbent lighting industry,with the Edison bulb at its heart, is well definedin terms of its supply chain, the divisions inSSL are less clear. “In the SSL value chain,boundaries are more blurred and the innova-tion cycle is more rapid,” said Chipalkatti.

Chipalkatti is also the chairman of the SSLsection of the lighting systems division withinthe National Electrical Manufacturers Asso-ciation in the US. Another industry associa-tion that he is closely involved with, andwhich is tied to one of the leading academicinstitutes involved in LED development, isthe Alliance for Solid-State IlluminationSystems and Technologies (ASSIST). Estab-lished in 2002 by the Lighting ResearchCenter at Rensselaer Polytechnic Institute inTroy, NY, ASSIST was set up to advance andpromote LED technology, and Chipalkattisees it as having a critical role in establishingthe required SSL industry infrastructure.

Whether these efforts and the rapid inno-vation in HB-LEDs mean that the light bulb’sdays are numbered seems very unlikely, how-ever. For the average consumer in the devel-oped world, lighting is an inexpensivenecessity that does not deserve or get muchattention. Changing that mindset will meanthat the SSL industry has to create a marketthat is different to the current one. The way todo this, believes Gasman, is by starting up anawareness campaign with consumers now, sothat HB-LED lighting becomes an “awaited”and desirable technology, rather than one thattakes the consumer by surprise.

The emphasis will need to be put on the fea-

tures that are unique to the technology, in par-ticular the precise control over wavelengthand brightness, as well as the ability to switchbetween different white-light “tones” at dif-ferent times of the day.

StandardsGasman also identified characterization stan-dards as a priority for the industry to address.“The industry stands in dire need of uniformstandards to measure the characteristics ofHB-LEDs,” thunders the NanoMarkets analy-sis. The old, existing standards, such as thecolor-rendering index (CRI), are simply notappropriate, it claims.

“Some experiments have indicated thathuman perception and liking for shades ofwhite does not conform to the CRI,” says thereport. “In fact, [they] suggest that our likingfor warm or cold white light varies accordingto the time of day and the ambient conditions.”

A definition of the lifetime of HB-LEDsmust also be agreed, says Gasman, who addsthat packaging and drive electronics shouldbe standardized. This fits in with Chipalkatti’svision of HB-LED light sources with a USB-type functionality.

For the HB-LED to ultimately prevail overthe Edison bulb, it appears that the industrywill need to address all of these issues whilesimultaneously solving the remaining tech-nological problems to increase chip bright-ness. Only then will we find out just howaccurate those optimistic long-range marketforecasts are.

Details of NanoMarkets’ report on HB-LEDscan be found at www.nanomarkets.net.

While the HB-LED industryfaces up to the challengesof developing a rivalinfrastructure, technologicalinnovation continues apace.Targeting general lightingapplications, this warm-white source is the latestproduct for residentialillumination manufacturedby Lamina Ceramics, and isbased on a combination ofred, green and blue high-brightness chips.

Lamina has made theheadlines in the past for its

development of ultra-bright-light engines thatemit several thousands oflumens and require amassive cooling system.

The company says that itsnew 95 lm source replicatesthe “warm-white” feel ofambient light in the home(3000 K color temperature),while emitting almost asmuch light as a 10 Whalogen bulb.

The US companybelieves that the appeal ofthe warm-white source willencourage residentiallighting designers andarchitects to mix solid-statelighting with conventionalbulbs and halogen sources.

White light for residential illumination

Lamina’s warm-white HB-LED is aimed at the home.

http://www.bruker-axs.com

WIDE-BANDGAP TRANSISTORS compoundsemiconductor.net

COMPOUND SEMICONDUCTOR DECEMBER 2005 23

WiMAX and WiBro emergeas major targets for GaN

Like many early-stage technological innova-tions, wide-bandgap transistors could legit-imately be described as a solution in search ofa problem. The power output, high-voltageand high-temperature operation of GaN, aswell as the robustness and reliability of SiC-based microelectronics, are all very impres-sive. Such devices have attracted lots ofattention and funding for research from themilitary sector, but genuine commercial appli-cations remain scarce.

While third-generation cellular was gener-ally regarded as the application that wouldusher GaN transistors into the mainstream,it now seems more likely that the emergingbroadband wireless access protocol WiMAXwill provide that opportunity. WiMAX (alsoknown as IEEE standard 802.16e) will haveto compete with many other broadband alter-natives, but could be the preferred last-milesolution in areas that are underserved by wiredbroadband or high-speed cellular coverage.

Kevin Linthicum, the chief technology offi-cer (CTO) at GaN transistor manufacturerNitronex, certainly believes that WiMAXoffers a big opportunity. The Raleigh, NC, com-pany – one of the pioneers in GaN microelec-tronics – has just released its first commercialproducts for the WiMAX market, having sam-pled them to customers for the past year.

GaN versus silicon LDMOSThe Nitronex strategy is to target the applica-tion areas where silicon LDMOS is weakest.“In chasing LDMOS we’ve given up tryingto compete on cost,” Linthicum told delegatesat the Key Conference in Palm Springs, CA,in early November. “What we need to do isfocus on areas where LDMOS might struggle.”

In practice, this means targeting high-frequency applications. Initially the WiMAXprotocol will operate at 2.5–2.7 GHz and3.4–3.6 GHz, with next-generation systemsset to use the 5.725–5.85 GHz band. Morespecifically, Nitronex is looking to penetrateapplications in WiMAX base stations rather

than target customer premise equipment.Crucially, Nitronex has already snared one

customer in the high-technology breedingground of Korea. In early 2006, RFHIC, acompany based in Suwon that sells RF com-ponents and modules, is expected to deployWiMAX products from Nitronex that featureits 50 W GaN-on-silicon transistors.

The power GaN HFET devices measure1 mm × 6 mm, and the chips feature a gateperiphery of 36 mm. The amplifiers producearound 70 W in continuous-wave power at28 V, with efficiency peaking at around 65%.Nitronex fabricates the devices by MOCVDto deposit a stress-mitigating transition layerbetween the silicon base and a 0.8 µm semi-insulating GaN buffer (figure 1). Linthicumsays that at the moment the full process givesNitronex a known-good-die yield of approxi-mately 75%, while the company has recentlyused field-plate technology to increase powerand gain characteristics.

Although Nitronex manufactures its GaNtransistors on a silicon base, the substrate

material is not quite the same as the conven-tional (100) crystal structure used in CMOSand LDMOS processing. Instead, Nitronexuses float-zone silicon with a (111) crystal ori-entation. The good news for Nitronex is thatthis is a scalable technology, and a futurechange to 6-inch-diameter wafers is expected.However, something that will prove moreproblematic for the company will be findinga toolset supplier that can provide GaN depos-ition equipment that is compatible with thelarger wafers.

This is because LED makers dominate theworld of GaN device manufacturing, and in thisbusiness much smaller substrates are typical.While pioneers such as Cree have begun theswitch to 3 inch production (Cree now makesabout 60% of its chips on 3 inch substrates),2 inch fabrication remains a common choice.

However, switching to 6 inch GaN-on-silicon will not be necessary to serve the require-ments of the relatively small WiMAX andW-CDMA base station markets, and moreapplications will need to be found to justify

New broadband wireless access protocols could provide a market for GaN transistors before anysignificant activity from the third-generation cellular business appears, writes Michael Hatcher.

The Korean company RFHIC says that early next year it will start to deploy power amplifierproducts that feature 50W GaN-on-silicon transistors developed by Nitronex (inset).

NIT

RO

NE

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compoundsemiconductor.netWIDE-BANDGAP TRANSISTORS

COMPOUND SEMICONDUCTOR DECEMBER 200524

any drive towards greater manufacturing vol-umes at the larger diameter.

At the moment it appears that the WiMAXdrive is being spearheaded in Korea, whichhas its own particular “flavor” of WiMAX,known as WiBro (short for wireless broad-band). The Korean communications companyKT Corporation is pioneering the deploymentof this standard, which uses the 2.3–2.4 GHzfrequency band.

KT joined the board of the WiMAX Forum,a global consortium pushing the technology,in November, and has since launched the firstcommercial WiBro service in Korea – ademonstration for industry executives anddignitaries at the Asia-Pacific Economic Co-operation’s annual event in Busan, south-eastKorea. The WiMAX Forum president, RonResnick, said of that development: “KT haslaunched the world’s first mobile broadbandnetwork that is based on the soon-to-be-ratified IEEE 802.16e standard, which is atthe core of mobile WiMAX.”

Products based on the WiBro standard areset to feature in the first mobile WiMAX sys-tems, with a release due in late 2006, andLinthicum says that the Korean market isalready exerting a considerable demand onNitronex technology.

“The WiMAX and military markets will bethe early adopters of GaN HFET power tran-sistors,” added Linthicum, who expects to seerevenue from these sectors within six months.Commercial deployment in W-CDMA basestations will take at least another 6–12 monthsto bear fruit, with the pace of design-insdetermined by the need to introduce newarchitectures and broader-bandwidth poweramplifiers (PAs). “The cellular market is veryconservative,” Linthicum said, indicating that

the likelihood of penetrating this sector withGaN technology may be even further off.

A matter of costCost will be one of the key factors that decideswhether or not GaN makes an impact. Directcomparison with silicon LDMOS is difficultto quantify, since the cost of silicon die can besuch a fast-moving target. For Linthicum, amore relevant comparison can be made withGaAs: “GaN will need to debut in the rangeof commercial GaAs PHEMT pricing in orderto be adopted in commercial markets,” he toldKey Conference delegates.

Of course, Nitronex is not the only companyto be targeting WiMAX applications with GaNamplifiers. Eudyna Devices sees WiMAX asa critical market for GaN, and the Japanesecompany has three product offerings in eachof the 2.5–2.7 GHz and 3.4–3.6 GHz bands,ranging from 30 W to 180 W output.

Oki Electric, a second Japanese companywith WiMAX in its sights, is taking a similarapproach to that of Nitronex. Oki says that thehigh-performance amplification of its GaN-on-silicon HEMT, which has a 56 GHz cut-off frequency and an fmax of 115 GHz, resultsfrom the use of a so-called recessed gate struc-ture (figure 2).

“We can contribute to the acceleration of WiMAX and next-generation wirelesscommunication systems,” said Oki’s CTO,Harushige Sugimoto. “Volume shipments ofsuch products are planned to start from 2007.”

While Oki and Nitronex are taking the sili-con route to cutting transistor cost, Eudynahas chosen a more radical approach to makingGaN devices more competitive. It plans toslash costs by using n-type SiC substratesdesigned for optoelectronic applications

AlGaN

GaN

GaN

transition layer

silicon

source draingate (0.7 µm)

AlGaN

transition layer

silicon

cap layer (15 Å)barrier of composition - x (26% Al)and thickness - d (180 Å)2 DEG (ns = 0.8 × 1013/cm2)

(µn = 1500 cm2/V-s)semi-insulating GaN buffer layer(0.8 µm)

stress-mitigating transition layer

high-resistivity silicon substrate

(10000 Ω-cm)

Fig. 1: Nitronex deposits a stress-mitigating transition layer on top of float-zone (111) siliconto fabricate its GaN HFETs. The chips will feature in WiMAX products in Korea in early 2006.

25COMPOUND SEMICONDUCTOR DECEMBER 2005

WIDE-BANDGAP TRANSISTORScompoundsemiconductor.net

instead of the conventional, and much moreexpensive, semi-insulating SiC material.

LED manufacturers grow GaN on top of n-type SiC, and by using an AlN layer grownby hydride vapor phase epitaxy beforeMOCVD of the active GaN layers, Eudynabelieves it has solved the twin problems ofparasitic capacitance and dielectric loss thatare met with the unconventional approach.

Eudyna’s Yasunori Tateno expects that thecost of devices can be drastically cut using thismethod (figure 3). “From a cost reductionpoint of view, we must use n-type SiC sub-strates,” he told Key Conference delegates.Tateno added that Eudyna was planning torelease devices manufactured on n-type SiCby the end of 2006. Initial results have beenimpressive, with amplifiers showing an out-put power of 101 W and a gain of 15.5 dB; butwhether Eudyna’s customers will be happy torely on the use of such unconventional materi-als remains to be seen.

Tateno was keen to emphasize the high effi-ciency of GaN HEMTs for W-CDMA cellu-lar applications, saying that if all 100,000 base

stations in Japan had their (relatively) ineffi-cient silicon LDMOS devices replaced withGaN-based PAs, the savings could be huge –both in terms of dollars and the environment.

“If total base station efficiency wasimproved from 15% to 25%, electricity con-sumption would be reduced by 400millionkWhours, equivalent to 600 million kg of CO2,”claimed Tateno. Such a wide-scale deploy-ment is far from a realistic scenario, partlybecause the key figure of merit is not only theefficiency of the PA chips, but the efficiencyof the entire system that is based around it.

Efficiency boostAt the Compound Semiconductor IC Sym-posium, which was co-located with the KeyConference, an improvement in GaN-based PAefficiency proved to be one of the most popu-lar talks of the week. Nitronex and researchersfrom the University of California San Diego(UCSD), collaborating with Qualcomm andNokia, described a W-CDMA base stationamplifier with overall power-added efficiencyof 50%, which is thought to be the highest fig-ure yet reported. “Measurement of the high-voltage envelope amplifier used in this workshows efficiency of 77% under W-CDMAsig-nals,” claimed the team. It concluded that com-bining GaN HFETs with advanced amplifierarchitectures would lead to “dramatic improve-ments” in base station PAs.

The key to the development is not just theuse of a GaN transistor from Nitronex, but alsothe advanced amplifier architecture that itenables. In the UCSD set-up, an envelope-tracking bias system improves both linearityand efficiency. The design means that theamplifier operates closer to saturation, withthe transistor maintained at a lower temper-ature. The dynamic peak voltage also reacheshigher values than can be used in a constantdrain bias voltage configuration.

According to Linthicum, envelope track-ing is just one of several advanced designs thatGaN transistors can enable. Others includeDoherty configuration Class F amplifiers, aswell as digital predistortion amplifiers.

While the combination of these novel archi-tectures and the material properties of GaNmay never quite knock LDMOS off of itspedestal in cellular applications, it appearsthat WiMAX is now the key application sec-tor for wide-bandgap RF microelectronics,and the one where its commercial viabilitywill first be proved. If WiMAX takes off, itcould be just the problem that GaN has beenlooking for.

Fig. 2: Oki Electric attributes the goodperformance characteristics of its GaN-on-silicon HEMTs to the use of a recessed gatestructure, which is said to reduce bothparasitic resistance and leakage current.

Fig. 3: According to Eudyna Devices, thebest way to cut the cost of GaN transistorsis to fabricate them using n-type SiCsubstrates. Eudyna’s Yasunori Tateno says that this approach will reduce theoverall cost of the device by as much astwo-thirds compared with conventionalsemi-insulating SiC substrates.

semi-insulatingSiC

substrateand epiwafer

packageand

assembly

n-typeSiC

GaN0.2 µm

GaN/AIN multilayer film

Si substrate AlN

source drain

gate

recessed andshortened gate

recessedohmic

SiNAlGaN

AIN

EU

DY

NA

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HIGH-POWER LEDS compoundsemiconductor.net

COMPOUND SEMICONDUCTOR DECEMBER 2005 27

Efficiency gains boost high-power LED performance

Until recently, market penetration ofhigh-power LEDs – defined asdevices operating at 1 W or more –

has been limited by performance and relia-bility concerns, as well as high deploymentcosts. But continuing improvements in lightoutput and the efficiency of light emission arenow yielding power LEDs that are starting tochallenge other lighting solutions in a rangeof applications.

Today’s power LEDs deliver 50–60 lm,enabling just 50 LEDs to produce the samelight output as a 3000 lm fluorescent tube.At the same time, luminous efficacy has risento around 60 lm/W, which far surpasses theperformance of incandescent bulbs and is fastapproaching the energy efficiency of fluores-cent lighting.

As a result, high-power LED manufactur-ers are now working to develop productsaddressing the general illumination market,which is currently valued at around $12 bn.However, real success in the mainstream light-ing market will require manufacturers toreduce the price of LEDs, while continuing todeliver steady improvements in the device’sluminous efficacy and total lumen output.

Increasing light outputIn theory, it should be possible to producemore light by simply driving bigger chips, typ-ically 1 × 1 mm, with higher currents. TheLuxeon III, for example, delivers up to 190 lmat red–orange wavelengths by drawing 1.4 A,compared with a flux of about 25 lm for typ-ical devices running at 350 mA.

However, most high-power LEDs convertonly about 15% of the input power into light,with the rest being lost as heat. And yet LEDsmust be protected from overheating, as sus-tained operation at high junction temperaturesreduces the device’s lumen output and shiftsits emission wavelength. Improving luminousefficacy is therefore essential for producingmore light from the same input power.

Continual advances in materials, fabrica-

tion techniques and device structures havealready produced LEDs with high internalefficiencies. The best red-emitting devicesbased on AlGaInP deliver internal quantumefficiencies (IQEs) approaching 100%, whileGaN-based green and blue light emittersdeliver IQEs of 50%, despite the large num-bers of dislocations formed during epitaxialgrowth on a foreign substrate.

Although efforts are continuing to improvethe IQE of GaN devices, larger gains in lumi-nous efficacy are expected to come fromincreasing the device’s extraction efficiency.In traditional LED chips, only a small pro-portion of the photons generated at the p–njunction leave the device. Since the semicon-ducting materials used to produce LEDs havea large refractive index, only those photonsemitted within typically 17° of the normaldirection can exit the chip’s front surface. Therest are trapped by total internal reflection andeventually absorbed by the material, leadingto heat generation rather than light extraction.

One particular problem for high-power

LEDs is that as the die area is increased, lightextraction efficiency falls. Data fromLumileds show that the external quantum effi-ciency (EQE) of both AlGaInP and AlInGaNchips falls by about 20% as the die area isincreased from 0.3 to 1.5 mm2 (figure 1). Thisis partly because light emission from thechip’s sidewalls is less effective for large-areadie, as photons have to travel much furtherbefore reaching a surface, which increasesinternal absorption. This means that it is essen-tial to improve the light emission efficiencyfrom the chip’s top surface.

Established techniques to increase theextraction efficiency include the use of a cur-rent-spreading layer, also known as a windowlayer, which ensures that light emission occursover the full area of the p–n junction. Manyleading GaN-based LED manufacturers alsoexploit a flip-chip geometry, with the devicemounted face-down, which allows light to beextracted through the substrate rather thanfrom the device’s top surface. As well as offer-ing higher extraction efficiencies, flip-chip

Designers are exploiting increasingly sophisticated strategies, such as surface roughening andincorporating photonic crystals, to boost efficiency and enhance light output. Susan Curtis reports.

60%

70%

80%

90%

100%no

rmal

ized

QE

@ 0

.5 A

/mm

2

0.0

AlGaInN/AI203AlGaInP/GaP

0.5 1.0 1.5 2.0 2.5die area (mm2)

~0.5 mm

~1.5 mm

Fig. 1. The quantum efficiencies of AlInGaN and AlGaInP chips fall significantly as the diearea is increased, mainly because less light is emitted from the sidewalls of the chip.

LUM

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Com

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CO M P O U N D SE M I C O N D U C T O R DE C E M B E R 200528

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29COMPOUND SEMICONDUCTOR DECEMBER 2005

HIGH-POWER LEDScompoundsemiconductor.net

assembly enables better thermal management,high-speed electrical interconnection, smallermodule sizes and higher reliability.

For AlGaInP chips, the GaAs substrateabsorbs all visible light, so either a reflectingstructure has to be inserted between the activeregion and the substrate, or, better still, theGaAs substrate has to be replaced with a trans-parent GaPcarrier. The use of transparent sub-strates, first pioneered by Hewlett-Packard(later Agilent) and now adopted by Lumileds,can deliver at least twice the luminous fluxof equivalent devices grown on absorbing sub-strates, but requires complex and expensiveprocessing technology to achieve wafer bond-ing with precise crystallographic alignment.

Texture and shapeSome chip manufacturers, notably Cree andLumileds, also enhance their LEDs’ exter-nal efficiency by shaping the die to reducereflections and increase light extraction.Lumileds’truncated-inverted-pyramid (TIP)geometry can yield extraction efficienciesapproaching 60% for AlGaInP chips, andR&D at the company indicates that TIP-LEDchips measuring 1 × 1 mm can offer efficaciesof 100 lm/W at 605 nm. However, TIP-LEDstructures are not suited to high-volumemanufacturing, and although some of the lightis extracted from the sidewalls, this emissionis less effective for larger chip areas.

Several other approaches have been devel-oped to combine high extraction efficiencieswith more scalable processing technologies.One of the most successful is the use of sur-face roughening, which reduces internalreflections and scatters the light outwards.Shuji Nakamura and colleagues at theUniversity of California, Santa Barbara, havecombined laser lift-off with photoelectro-chemical etching to produce regular cone-likefeatures on the surface of a flip-chip GaN-based LED (figure 2). The power output fromthese LEDs increases by a factor of 1.9 aftera 2 min etch, and 2.3 after a 10 min etch, com-pared with flat-surface devices.

Osram Opto Semiconductors has incorpo-rated this concept into its latest generationof thin-film LED chips. Thin-film technology,which involves bonding the LED to a metal-lized carrier substrate before the original sub-strate is removed, offers a simpler, lower-costalternative to transparent substrates, but onits own it does not deliver a high EQE. In theOsram approach, inclined microreflectors areformed in the top part of the epitaxial layer,before the structured surface is covered with

mirror layers and bonded to the carrier. Thebonding interface need not be optically trans-parent, which allows the use of metal-to-metal bonding.

Tests indicate that the luminous flux fromOsram’s buried-microreflector LEDs is up to70% higher than that from thin-film LEDs pro-duced without microreflectors. The com-pany’s thin-film technology is already beingexploited in its latest product release, the high-power Ostar LED. This 5 W device incorpo-rates four thin-film chips measuring 1×1mm2,and the RGB version emits more than 120 lmfrom a package measuring 3 × 1 cm2, with thelight source consisting of one red, one blue andtwo green thin-film chips.

More sophisticated approaches to improv-ing LED extraction efficiency include the useof a 2D photonic crystal, a regular array of

100–250nm diameter holes formed in the cur-rent-spreading layer to guide light to thedevice’s surface. This approach has been inves-tigated by Sandia National Laboratoriesresearchers in collaboration with Lumileds toimprove the efficiency of blue GaN-basedLEDs – in small-area LEDs (~0.036mm2) theyhave reported a two-fold increase in brightness.

However, these small devices suffer fromedge effects that limit the improvements thatare theoretically possible with photonic crys-tals, while fabricating large-scale photonicstructures remains a challenge. Currentdevices rely on electron-beam lithography,while research is continuing on new process-ing techniques that will enable the rapid pat-terning of large areas.

For example, Steven Brueck at the Univer-sity of New Mexico has been developing alithography technique that exploits interfer-ence between coherent optical beams to cre-ate a periodic pattern in a single large-areaexposure that takes just a few seconds. A1 mm2 GaN-based LED produced by thismethod has been shown to deliver uniformlight emission, but efforts are still underwayto evaluate the effect of the photonic structureon the quantum efficiency of the device. Workis also continuing to produce a better engi-neered, full-wafer patterning tool.

Microcavity LEDsIncreases in light output can also be producedwith microcavity LEDs, which are expectedto yield high extraction efficiencies from pla-nar, rather than shaped, LED devices. Planardevices are particularly important for telecom-munications applications, in which the lightemitted from the LED must be coupled into anoptical fiber with a typical core diameter of100µm. However, the EQE of standard planarLEDs that do not contain a microcavity is typ-ically limited to a few percent, even whenencapsulated in an epoxy dome.

Microcavity LEDs exploit optical confine-ment between two mirrors to modify the angu-lar pattern of light emission, causing a largefraction of the light to be emitted into a reso-nant mode almost entirely contained in theextraction cone (figure 3). For example,researchers at Infineon Technologies inGermany and the Ecole PolytechniqueFédérale de Lausanne in Switzerland havefabricated a microcavity LED in aGaAs/AlGaAs device by forming distributedBragg reflectors (DBRs) either side of theactive region. This device’s EQE was 14%into air and 20.6 % with encapsulation into a

n-electroden-GaN

p-GaN

Au/Sn

Ti/AuSi submount

InGaNactive region

p-electrode

Fig. 2. A flip-chip GaN structure can betreated with laser lift-off and wet etching(top) to produce cone-like features on thesurface (centre). Such devices deliver atleast a two-fold increase in relative powercompared with flat surface LEDs (bottom).

50 60403020100current (mA)

pow

er (a

.u.)

10 min etching2 min etchingflat surface

500 nm

UC

SB

HIGH-POWER LEDS compoundsemiconductor.net

COMPOUND SEMICONDUCTOR DECEMBER 200530

lens-shaped epoxy dome. Scientists at University of California, Santa

Barbara, and the Ecole Polytechnique inPalaiseau, France, have calculated that theextraction efficiency from planar microcavityLEDs could reach 40%, provided that the struc-ture’s thickness and composition is controlled

with the required precision. Since most of thenon-extracted light is trapped in lateral guidedmodes, the researchers believe that incorpo-rating photonic-crystal structures into micro-cavity LEDs could further improve the EQEby scattering light towards the device’s surface.

Agroup at Sandia National Laboratories are

also investigating this type of device in a two-year project that began at the end of 2004. Theresearchers plan to fabricate and test InGaNLEDs that combine a 400–460 nm photonicstructure with a planar microcavity formed byconductive GaN/InGaN DBRs with the ulti-mate aim of doubling the device’s EQE.

standard LED microcavity LED

extraction cone

source

next

nin nin

isotropic source modified emissionmirrorR~100%

~λ

mirrorR~60%

Fig. 3. In a standard LED (left) light is emitted isotropically from the source, but in amicrocavity LED (right) the two closely-spaced mirrors that confine the light funnel a largeproportion of the emission into an extraction cone.

This article is based on the findings of LEDQuarterly Insights, a subscription servicefrom the publishers of CompoundSemiconductor that provides regularanalysis of the critical technologyinnovations and commercial opportunitiesin the highly dynamic LED industry. Overthe year, the service will produce fourreports that provide detailed commentaryon high-power LEDs; performance andstandards; white LEDs; and packaging andoptics. LED Quarterly Insights is part of theTechnology Tracking programme. For moreinformation see www.technology-tracking.com.

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MATERIALS & EQUIPMENT NEWS compoundsemiconductor.net

COMPOUND SEMICONDUCTOR DECEMBER 2005 31

Oxford has access toatomic layer patentsASM International has granted a license thatgives UK-based equipment manufacturerOxford Instruments Plasma Technology(OIPT) access to its atomic layer deposition(ALD) technology.

The agreement covers more than 280 issuedand published patents, and will enable OIPTto develop new products and processes.

ALD can be used to deposit extremely thinfilms, to make micromechanical devices, andhas applications in semiconductor processing.

Matheson reshufflesSpecialty gas and gas-handling equipmentsupplier Matheson Tri-Gas has reorganizedinto four separate business units.

These are: industrial gases; electronicgases; specialty gas and equipment; and theAsian business organization.

Trikon seals mergerTrikon shareholders have approved the UKplasma etch and deposition equipment sup-plier’s merger with Aviza Technology. Thecompany will operate under the Aviza name.

CMP systemLogitech LtdThe CDP system from Logitech Ltd (Semicon Japan, booth 8A-101) isideal for global planarization of III-V wafers and delayering ICs/MEMSdevices for fault analysis and reverse engineering.The fully automatedcontrol panel allows process parameters to be stored for future use,helping ensure end-result repeatability. This, coupled with a low cost ofownership, makes the CDP particularly useful for testing new CMPslurries, pads and templates for off-line analysis and for off-line trials ofnew CMP processes without stopping production runs.

Contact: Logitech Ltd, ErskineFerry Road, Old Kilpatrick,Glasgow G60 5EU, Scotland, UKTel: +44 1389 875444Fax: +44 1389 890956E-mail: info@logitech.uk.comWeb: www.logitech.uk.com

PraxairNew Sure Flow Bulk Specialty Gas SystemsPraxair Electronics SureFlow Bulk Specialty Gas Supply (BSGS) systemsand controllers are designed for cost-effective, safe, reliable gasdistribution. Count on our global experience in implementing BSGSsystems to meet the flow rates required by larger sites. Our gas engineersprovide unique system solutions that safely deliver high flow rates with

the flexibility and redundancyrequired for increased uptime. Byupfront modeling of your specificapplication, our engineers candesign a system to work flawlesslyand give you the piece of mind forsecure operations.

Contact: Jack ErbTel: +1 210 489-5827Fax: +1 210 489-5867Web: www.praxair.com/electronics

EngisOptimized Surface PreparationHigher levels of precision control are now achievable in the planarization,delayering and polishing of advanced materials and substrates forcompound semiconductors, thanks to the new MPC surface preparationsystem from Engis-Microtech.Incorporated into the MPC’s integral machine design is a 6-Sigmacapability for material removal, flatness and surface finish generation. Themenu-driven microprocessor controls enable operators to fully optimizeany polishing, delayering or planarization process. Plus, the MPC’s

oscillation system provides 3-axismotion for true CMP kinematics.

Contact: Engis Corporation105 W HINTZ RdWheeling, IL 60090 USATel: +1 847-808-9400 Fax: +1 847-808-9430E-mail: microtech@engis.comWeb: www.engismicrotech.com

Osram Opto SemiconductorsPromotion to power With two to three times the output and five times the life span, the new6-lead MultiLEDs from Osram Opto Semiconductors leave theirpredecessors firmly in the shade. All three chips (red, green and blue) arefabricated using thin-film technology and allow almost all the light to beemitted at the surface. This results in high optical efficiency and newapplications, such as advertising and effect lighting. The optical efficiencyof the brightest generation of chips of this size is 43 lm/W for red, 36 lm/W

for green and 11 lm/W for blue.

Contact: OSRAM OptoSemiconductors GmbH,Wernerwerkstr. 2, D-93049Regensburg, GermanyTel: +49 941 850 3535Fax: +49 941 850 444 3535E-mail: tanja.gassner@osram-os.comWeb: www.osram-os.com

PRODUCT SHOWCASETo advertise your product in this section, contact Joanna Hook on tel: +44 117 930 1028, or e-mail: joanna.hook@iop.org.

Taiwan-based Huga Optotech hasinstalled a Thomas Swan MOCVD reactorto make blue and green GaN-based LEDs. Azzurro Semiconductors, a Germany-based maker of 6 inch GaN-on-siliconwafers, has ordered a Thomas Swanreactor that features an EpiCurve wafercurvature sensor from LayTec. France-based MBE equipment supplierRiber has installed a research machine atKorea’s biggest laboratory, the Electronicsand Communications Research Institute.

Equipment sales

RESEARCH REVIEW compoundsemiconductor.net

COMPOUND SEMICONDUCTOR DECEMBER 200532

Researcher Sylvain Joblot from STMicroelectronics and co-workers atFrance’s CNRS research lab have grown GaN HEMTs on silicon (001)substrates, which they claim are better suited to the mainstream siliconindustry than the silicon (111) substrates used by GaN-on-silicon HEMTmanufacturers Picogiga and Nitronex (Appl. Phys. Lett. 87 133505).

Silicon (001) substrates offer the same advantages for GaN HEMTmanufacture, in terms of the combination of low cost and high thermalconductivity, as silicon (111) substrates that have already been used toproduce transistors. However, because silicon (001) substrates are widelyused by the silicon industry, transistors fabricated on the material aremore suitable for integration with mainstream microelectronics.

However, several difficulties are associated with the growth of GaNlayers on silicon (001) substrates. A large lattice mismatch (–16.2%)and a 113% difference in thermal expansion between silicon and GaNcan lead to cracking of the epitaxial layers, a high density of disloca-tions, and the growth of undesirable domains of cubic GaN alongsidethe wurtzite form of GaN that is required.

Now Joblot and colleagues have managed to develop an MBE

process to produce crack-free GaN-based heterostructures on high-resistivity 2-inch silicon (001) substrates mis-orientated by 5° towardsthe [110] direction. After annealing the substrate at temperatures of upto 1150 °C to remove the native oxide layer, they grew an 80 nm-thickAlN buffer layer and a stack of 250 nm GaN and AlN layers on thesubstrate, followed by a 600 nm GaN layer, a 25 nm AlGaN barrierand a 1 nm GaN capping layer.

Profiling a 10 × 10 µm area of the epiwafer’s surface with an atomicforce microscope revealed that the layer’s surface roughness was typ-ically 9–10 nm, while transmission electron microscopy images deter-mined that the epiwafer had a threading dislocation density of5–10 × 1010 cm–2. X-ray diffraction measurements suggested that thestructure contained only the wurtzite form of GaN.

HEMT devices were fabricated from the epiwafer, with aTi/Al/Ni/Au stack forming the ohmic contacts. By measuring the sheetresistance of Hall bars and transmission line model devices, the teamestimated that the transistor had a room temperature electron driftmobility of 730 cm2/Vs at zero gate voltage.

001silicon improves GaN integration

MOXtronics, a developer of devices based on ZnO and its alloys, hasfabricated ZnO ultraviolet photodiodes and p-type FETs in partner-ship with Henry White’s group at the University of Missouri, and SouthKorea’s Seoul National University and Jeonbuk National University(Appl. Phys. Lett. 87 153504).

The team claims that these achievements demonstrate that ZnO canbe used to fabricate a wide range of devices, as well as showing thatarsenic is a good dopant for creating the p-type form of this material.

ZnO devices are of interest because they are suitable for use in harshenvironments such as nuclear reactors and space. The material has ahigher radiation resistance than silicon, GaAs, SiC or GaN.

The photodiodes and FETs were grown by hybrid beam deposition(HBD), a technique which allows solid, vapor and gas source materi-

als to be used for crystal growth. According to MOXtronic’s YungryelRyu, HBD was used because conventional growth methods, such asMBE and CVD, are unsuitable for producing high-quality ZnO crys-talline films.

The team’s ZnO photodiode has a peak sensitivity at 380 nm, andhas a dark current below 10–6 A/cm2. This indicates that it has the poten-tial to detect ultraviolet light with low noise. Ryu says that MOXtronicswill release ZnO-based commercial ultraviolet detectors in 2006, andthat these will have a sensitivity three times higher than that of anyother solid-state ultraviolet detector.

The ZnO MESFET produced by the collaboration has carrier mobil-ities of over 1000 cm2/Vs. “These large mobilities make ZnO a strongcandidate for high-speed devices,” remarked Ryu.

MOXtronics makes ZnO photodiodes and transistors

Scientist Glenn Solomon from Stanford University, in collaborationwith US-based CBLTechnologies and the Paul Drude Institute for SolidState Electronics in Berlin, Germany, has produced GaN-on-sapphireepiwafers in a single chamber using a combination of MOCVD andhydride vapor epitaxy (HVPE) (Appl. Phys. Lett. 87 181912).

The team claims that the method offers a cost-effective and scalablemeans for production of GaN-based epilayers and devices, withoutthe need for a separate reactor for each deposition step.

The approach enables growth of a high-quality GaN buffer layer at500 °C by MOCVD, followed by the deposition of a thick GaN layerat 1025 °C at a much higher growth rate using HVPE.

The hybrid reactor uses an internal substrate heater (cold-wall heat-ing system) for MOCVD growth, in the form of resistive heaters inthe susceptor, and a hot-wall system for HVPE, using a multizone tubefurnace (see figure above).

The researchers deposited a 25 nm buffer layer on a 2-inch (0001)sapphire substrate at 500 °C by MOCVD, before using HVPE to growa 12 µm-thick GaN layer at a rate of 25 µm/h.

Atomic force microscopy measurements of a 10 x10 µm region ofthe sample’s surface revealed a surface roughness, in term of the root-mean-square value, below 1 nm. Transmission electron microscopyimages showed that the dislocation density decreased with distancefrom the buffer layer, and had an average value of 107/cm2 for the mate-rial within 1 µm of the epiwafer’s surface.

Complementary techniquesoffer better route to growth ofGaN-on-sapphire epilayers

substrate

GaCl GaexhaustHCINH3MO

A combination of an external tube heater and internal substrate heaterallows GaN growth by both MOCVD and HVPE in the same chamber.

http://www.optotaiwan.com

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