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Crystal GrowthLaboratoryYour Competent Partnerin Crystal Growth andSolidification Processes

Annual Report 2003

- Equipment and Process Development -- Optical and Electrical Characterization -

- Numerical Modeling -

Content

contact: [email protected]

Structure

Overview

Research Fields

Low defect InP substrate crystals

Development of growth of processes for GaN substrates

CaF2 crystals for microlithography: Influence of oxygen

Low cost Silicium for photovoltaic applications

Chalcopyrite semiconductors for thin film solar cells

The CrysVUn3D framework

Soft-computing in crystal growth

Modeling of melt convection by 2D – 3D coupling

Modeling the dynamics of dislocations

The virtual Material Science Laboratory onboard theInternational Space Station

Staff

Publications

Equipment

Contact

Structure

Bulk Crystal Growth of Optical Materials

• CaF2 Crystals for Lenses in DUV Microlithography

• Oxides for High Speed Communication and Medical Applications

Materials for Solar Cells

• Low Cost Silicon • Thin Films of Copper-

Indium-Diselenide (CIS)

Software Development• Process and Defect Models• 3D Simulation• Advanced Mathematical or

Numerical Methods• Graphical User Interface

Thermal Modeling• Bulk Crystal Growth and

Alloy Solidification• Licensing of Software

Products

Bulk Crystal Growth of Wide Band Gap Semiconductors

• Solution Growth of GaN for Lasers, LEDs and UMTS

Bulk Crystal Growth of “classical” Semiconductors

• Silicon for Microelectronics• Low Defect GaAs and InP for

High Power Laser Diodes and High Speed Electronics

Crystal Growth Laboratory

Overview


Crystal growth processesprovide basic materials formany applications and are forexample one key technology inthe chain of all manufacturingprocesses for (opto-)electronicdevices. The research anddevelopment of crystal growthprocesses is driven by thedemands which come from thespecific applications; but incommon there is a need for anincrease of crystal dimensions,improved uniformity of therelevant crystal properties in themicro- and macroscale andmaterials with new properties.

Therefore, the focal area ofresearch of the Crystal GrowthLaboratory (CGL), is to develop– in close collaboration withindustry - equipment andprocesses for the production ofbulk crystals and thin films inorder to meet the increasingrequirements on crystal qualityand cost reduction.

The strategy of CGL is to

optimize the crystal growthprocessing by a combined useof experimental processanalysis and computermodeling. This activities arebased on a suitableexperimental infrastructure andon highly efficient user friendlysimulation programs namedCrysVUn, STHAMAS andSTHAMAS3D. These computercodes, which are continuouslyfurther developed, are used forand by the industrial partners todevelop crystal growthequipment and processes.

CGL was founded at theDepartment of MaterialsScience of the University ofErlangen - Nuremberg by Prof.Dr. Georg Mueller in 1979.Since 1996 the Crystal GrowthLaboratory has established theworking group "Crystal Growth"at the Fraunhofer Institute forIntegrated Systems and DeviceTechnology (IISB) in Erlangen.This working group became theDepartment Crystal Growth in

autumn 1999.

Since the foundation of CGLmore than 200 papers inscientific journals andconference proceedings havebeen published. Furthermore,CGL has educated a lot ofexperts in this field. 117 "Study"theses, 82 diploma theses and36 PhD theses may serve as areference for this.

More than 90% of funding ofCGL results from researchcontracts directly with industrialpartners and with the GermanMinistry for Research andDevelopment, the BavarianResearch Foundation, theBavarian Government, theGerman Research Foundation(DFG). Since 1996 almost 12Mio. Euro have been acquiredfrom the different sourcesindicated above.

Today, CGL consists of morethan 30 highly motivatedcoworkers. They are experts in

Fig. 1: German Science Foundation award of the Stifterverband was granted to Prof.Müller, Dr. Friedrich, Mr. Molchanov, Mr. Gräbner, Dr. Ardelean (from left) and

coworkers of Schott Lithotec

Overview


different fields, e.g. systemsengineering, metrology,computer simulation, physics,material science, mathematics.

In the year 2003 the R&Dactivities of CGL weredecorated with several nationalawards. Which underlines thefact that CGL is a world-wideacknowledged center ofcompetence in this field. Theresearch award of the GermanAssociation for Crystal Growth(DGKK) was granted to Dr.Birkmann for his outstandingachievements in the field of“growth and characterization ofSilicium doped GaAs substratecrystals with extremely lowdislocation densities”. Dr. Jung,Mr. Hainke and Mr. Jurmareceived the Georg-WaeberInnovation Award from the“Förderkreis Mikroelektronik” fortheir outstanding contributionsin the field of “development andcommercialization of thesoftware program CrysVUn forthe optimization of crystalgrowth processes inmicroelectronics”. During theFestival of Research of theFraunhofer Society, held onOctober 22 2003 in Duisburg

the German ScienceFoundation Award of theStifterverband was granted toDr. Ardelean, Dr. Friedrich, Mr.Gräbner, Mr. Molchanov andProf. Müller. The price wasawarded to the researchers fortheir constitutions to thesuccessful growth of highlyperfect calciumfluoride crystalsto be used in semiconductortechnology as lens material inthe micro lithography forproducing chips.

These scientific achievementsare also one reason that thedepartment could continue itsindustrial collaborations in itstraditional fields despite of theeconomic contractions of theglobal market.

In addition, the basis was madein 2003 so that the newresearch areas could beextended further. In the field ofsolution growth of GaN-crystalstransparent GaN was grownreproducibly. In the area of lowcost silicium for photovoltaicapplications a new R&D projectwas initiated with the companyRWE Schott Solar. In thisproject the carbon transport is

investigated during the pullingof Silicium octagons withlengths of up to 7 m and wallthickness of a same-hundredmicrons.

In the field of numericalsimulation the IISB is the firstinstitution which utilizes newmethods from the field of soft-computing like the geneticalgorithms in order to optimizeautomatically crystal growthequipment and processes. Thisis one of the prerequisites, thatthe software products of theCGL will be used by the crystalgrowth companies in the future.

CGL maintains national but alsointernational cooperations toindustry. The industrial partnerswere in 2003 (in alphabeticalorder): Crystal GrowingSystems, EADS, FreibergerCompound Materials, Komatsu,LG Siltron, Linn High Therm,MA/COM, MEMC,Photonicmaterials, SchottLithotec, Shell Solar, Shinetsu,Sumco, Riedhammer, RWESchott Solar, VB-TEC,Umicore, Wacker Siltronic,Wafer Technology.

Fig. 2: The Georg Waeber Innovation Award was granted to the CrysVUnteam, consisting of Flaviu Jurma-Rotariu, Marc Hainke, Thomas Jung and

former co-workers of CGL.



Indium phosphide is a III-Vcompound semiconductorcrystallizing in the sphaleritestructure. The revolution inoptical fiber communicationshas swept InP into a dominantposition as substrate for opto-electronic devices. InP has afortuitous lattice match to alloyswith bandgaps coinciding withthe 1.3µm and 1.55 µmwindows in optical fiber. Forlattice-matched growth ofternary alloys InGaAs andInAlAs and quarternaryInGaAsP and AlInGaAs, InP isthe substrate of choice.Heterostructure devices basedon these alloys, by virtue oftheir bandgaps, provide astrong driving force for bulk InPcrystal growth development.

During the past twenty-fiveyears, as the growth of InPsingle crystals has gone from alaboratory curiosity to acommercial process, many newapplications for InP substrateshave emerged. The mainstay ofdemand continues to be in thefield of telecommunications, butother uses for InP materialinvolving high speed electronicand photonic circuits havearrived. In addition to highfrequency, wirelesscommunications, broadband

gigahertz radar has beenachieved using InPphotoconducting antennas.

The state of the art for InPcrystal growth is dividedbetween three competingtechnologies; the Liquid-Encapsulated-Czochralski-Technique (LEC) and theVapour-Pressure-Controlled-Czochralski-Technique (VCZ)with top seeding and verticalgrowth in a container withbottom seeding by the VerticalGradient Freeze (VGF) orVertical Bridgman (VB)Technique. The pulling methodhas generally been the mostcost effective, but itsdisadvantage is the highdislocation density caused byhigh levels of strain duringgrowth. On the other hand,vertical container growth offersa very low dislocation densitybecause of its low-stressenvironment. But it is plaguedby yield problems due totwinning and interfacebreakdown in heavily dopedcrystals.

In our laboratory S- and Fe-doped 2” crystals are grown bythe VGF-technique in [001]-direction. The crystal growthprocess was optimized by using

a “flat-bottom” crucible.Thereby, an optimized furnaceset-up with a high thermalstability was developed by theaid of numerical modeling usingthe software package CrysVUn.

For the growth of S-doped InPLEC-grown seed crystals withan EPD = 3-5·104 cm-2 wereusually used. In this case a hightendency to polycrystallinegrowth was observed. Toincrease the single crystallineyield, LEC-seed crystals withEPD < 1000 cm-2 were appliedfor the first time.

The samples cut from thegrown VGF-crystals werecharacterized by Hall-measurements, dislocationrevealing and synchrotron X-raytopography. In the VGF-crystalsthe dominant type ofdislocations is represented by60°-dislocations (type (1)).Additionally edge-dislocationswith line vector l = <112> (type(2)) were found at the seed end(see fig. 1). In the case of LEC-seed crystals with EPD < 1000cm-2 a sudden increase of thedislocation density at theseeding interface wasobserved. In the VGF-grownsection of the crystal the EPD is7500 cm-2 (see fig. 1). It is

Fig. 1: X-ray topogram of a vertical section cut from a 2” InP crystal grown by the VGF-method. Thedislocation density of the LEC-seed is < 1000 cm-2. In the VGF-grown section of the crystal the EPD is7500 cm-2. 60°-dislocations (type (1)) and edge-dislocations (type (2)) with line vector <112> werefound near the seeding interface (s).



assumed that dislocations with l= <112> are formed by grow-inand misfit-dislocations. 60°-dislocations can be related tothermal stress. However, thedislocation density decreaseswith increasing dopantconcentration (n > 1.5·1018 cm-

3). At the tail end of the crystalsan EPD of 500 cm-2 is reached(see figure 2 a).

The growth of Fe-dopedcrystals is under development.The single crystalline yield isreduced by polycrystallinegrowth and twinning. Fig. 2 b)shows an EPD-mapping of a 2”substrate from the seed end ofa Fe-doped crystal. The EPD is16000 cm-2.

Recent Publications

U. Sahr, I. Grant, G. Müller,Conf. Proc., 13th Int. Conf. onIndium Phosphide and RelatedMaterials 2001, Nara, Japan,533-536, IEEE: ISBN 0-7803-6700-6

U. Sahr, M. Baeumler, I. Grant,W. Jantz, G. Müller, Conf.Proc., 14th Int. Conf. on IndiumPhosphide and RelatedMaterials 2002, Stockholm,Schweden, 405-408, IEEE:ISBN 0-7803-7320-0

I.R. Grant, U. Sahr, Conf. Proc.,14th Int. Conf. on IndiumPhosphide and RelatedMaterials 2002, Stockholm,Schweden, 413-415, IEEE:ISBN 0-7803-7320-0

U. Sahr, G. Müller, Conf. Proc.,12th International Conferenceon Semiconducting andInsulating Materials 2002,Smolenice Castle, Slowakei,13-18, IEEE: ISBN 0-7803-7418-5

M. Baeumler, E. Diwo, W.Jantz, U. Sahr, G. Müller, I.Grant, Conf. Proc., 29thInternational Symposium onCompound Semiconductors2002, Lausanne, Schweiz, 53-56, IOP Conference Series 174

a)

b)

Fig. 2: EPD-mappings of 2” substrates. Figure a) represents asubstrate from the tail end of a S-doped crystal (EPD = 500 cm-2). Infigure b) a substrate from the seed end of a Fe-doped crystal isshown. The EPD is 16000 cm-2.

Development of growth of processes forGaN substrates


Both the commercial and thescientific success achievedinternationally in thesemiconductors belonging tothe group III-nitrides continued.First nitride based laserdiodeshave been incorporated intocommercial products and alsoin the areas of high temperatureand high frequency electronicsmajor progress has been madee.g. for the breakdown voltageand the gate leakage currents.

Despite all progress the devicesare still grown by heteroepitaxywhich gives rise to a number ofproblems. A GaN single crystalof relevant dimensions is still notin sight. Nevertheless there is alarge progress concerning the

so-called quasi-substrates(freestanding layers grown byhydride vapor phase epitaxy).The dislocation densities are inthe best case as low as 106cm-2,which is still significantly higherthan in the case of the classicalIII/V-semiconductors.

At CGL research is done on thecrystal growth of GaN in theframe of a BMBF-fundedproject (FKz. 01BM158). Themain point of interest is atechnique which allows thegrowth of GaN crystals from ametallic flux. The nitrogen issupplied by the vapor phase.

The project work advanced verymuch during the last year.

Prototype facilities for thecrystal growth of GaN havebeen developed and were putinto operation. In these set-upsGaN-crystals were grown in theflux by homogeneousnucleation. In addition, it wasalso possible to grow GaN byheterogeneous nucleationusing a seed.

By optimization of the processparameters we succeeded tonearly completely suppress theoccurrence of structural defectsin form of pits on the crystalsurface. At present there are nodefects of this type visible in thescanning electron microscope.

Apart from the crystal growth

Figure 1: GaN crystals grown from flux

Development of growth of processes forGaN substrates


various non destructivemethods like Raman-spectroscopy, opticalabsorption and cathodo- andphotoluminescence (PL) havebeen used to characterize thecrystals.

The Raman-spectra (fig.2a)show the characteristic peaksfor GaN and allow to estimatethe charge carrier concentrationto be in the order of 1019 cm-3. Amore precise quantification bymeans of electricalmeasurements will follow.

A photoluminescence spectrumbetween 1.8 and 3.6 eV of asample grown by the methoddescribed above is shown infig.2b. The spectrum is typicalfor highly-doped n-type GaN. Itshows a luminescence close tothe band gap between 2.9 and3.4 eV and a yellowluminescence peak between1.8 and 2.6 eV.

In 2004 the work on the solutiongrowth of GaN will beintensified. It is aimed tocorrelate crystal quality andgrowth conditions by applyingcomprehensive electrical andstructural characterization. Thiswill help to further improve theprocess conditions.

One of the main problemsconcerning the growth of nitridecrystals is the fact that thenitrogen solubility is unknownunder the conditions of theapplied process. Therefore, it isplanned to determine thenitrogen solubility by usingthermogravimetry (TG).Meanwhile we succeeded tooptimize the thermogravimetrysystem of the company Netschso far, that the specifications ofthe manufacturer are exceededand that the accuracy should be

sufficient for the determinationof the solubilities. Firstquantitative results areexpected for 2004.

Besides the growth of GaNfrom metallic fluxes we startedin a cooperation with theTechnical Chemistry of theuniversity Erlangen Nurembergto perform R&D work on thecrystallization of GaN fromsupercritical NH3. A similarmethod is successfully used inindustry since decades for thegrowth of quartz crystals for

technical applications fromsupercritical water.

500 550 600 650 700 750 800

A1(LO)

E2

A1(TO)

1,8 2,0 2,2 2,4 2,6 2,8 3,0 3,2 3,4 3,6

a)

b)Raman-Shift in cm-1

Inte

nsity

in a

.u.

Inte

nsity

in a

.u.

E in eVFigure 2a) Raman spectrum of flux-grown GaN

2b) PL-spectrum of flux-grown GaN

CaF2 crystals for microlithography:Influence of oxygen


Single crystalline calciumfluoride (CaF2) is designated asa lens material for thephotolithography atwavelengths in the deepultraviolet region. Theprerequisites for this applicationare a high transmission and ahigh resistance with respect toradiation damage under highintense laser irradiation. PureCaF2 has excellenttransmission properties withoutabsorption bands over a widewavelength range from UV toIR. Selective absorption bandsexist in CaF2 only if the crystalcontains impurities.

Oxygen is considered as amajor impurity in CaF2. It isreported in literature thatoxygen in CaF2 leads to theformation of color centers whichstrongly reduce the radiationhardness. But so far noquantitative relationshipbetween the oxygenconcentration in the crystal andits optical properties has beenreported.

Experimental

The influence of oxygen on theoptical properties of CaF2 wasinvestigated by special crystalgrowth experiments. Theexperiments were carried out ina special Bridgman-type growthfacility at CGL. Theexperimental set-up isschematically shown in fig. 1. Aspecial gas supply system wasused to introduce oxygendirectly into the crucible duringcrystal growth. The flow rate ofoxygen was controlled bymass-flow-controller. Theconcentration of the oxygen inthe growth atmosphere andtherewith in the crystal wasvaried over a wide range during

growth.

After growth the oxygenconcentration in the CaF2crystal was determinedquantitatively by a specialcharacterization techniquecalled ERD (Elastic RecoilDetection). Concentrationsbetween 5 ppm and 150 ppmwere detected.

Investigations of the opticalproperties of the CaF2 crystal

revealed that the oxygencauses an increase of theabsorption in the UV range withan absorption maximum at 197nm (fig. 2a). The relationbetween the oxygenconcentration in the crystal andthe absorption coefficient at 197nm was found to be linear (fig.2b). This calibration relation canbe used for a quantitativedetermination of the oxygenconcentration in CaF2 crystalsby absorption measurements.

Fig. 1: Experimental set-up for growth of oxygen doped CaF2crystal.

CaF2 crystals for microlithography:Influence of oxygen


Furthermore, the influence ofoxygen on the radiationhardness to X-ray and toexcimer F2-laser (157 nm)irradiation was examined. X-rayirradiation of CaF2 containingoxygen induces absorptionbands in visible range with amain maximum at 375 nm.Thereby, the X-ray inducedabsorption in CaF2 increaseswith increasing oxygenconcentration.

Recent PublicationsA. Molchanov, O. Graebner, G.Wehrhan, J. Friedrich, G.Mueller, Optimization of thegrowth of CaF2 crystals bymodel experiments andnumerical simulation Journal ofthe Korean Crystal Growth andTechnology 13 (2003) 15-18

A. Molchanov, U. Hilburger, J.Friedrich, M. Finkbeiner, G.Wehrhan, G. Mueller,Experimental verification of thenumerical model for a CaF2crystal growth process CrystalReseach and Technology 37(2002), 77-82

A. Molchanov, U. Hilburger, J.FriedrichThermoelementanordnung zurTemperaturmessung inchemisch agressiven Medienund bei Temperaturen größer1000°C, Deutsches Patent,Amtsaktenzeichen: 101 06475.6

A. Molchanov, U. Hilburger, J.FriedrichTemperaturmessanordnung fürden Einsatz in chemischagressiven Medien und beiTemperaturen größer 1000°CDeutsches Patent,Amtsaktenzeichen: 101 06475.4

Fig. 2: Influence of oxygen concentration on absorption coefficient ofCaF2 crystal.

Low cost Siliciumfor photovoltaic applications


One of the great challenges inthe solar cell industry is thereduction of the productioncosts while maintaining orincreasing the cell efficiency.The Crystal Growth Laboratoryis involved in the research ofseveral industrial processeshaving this goal in mind.

On the one hand theoptimization of the so-called Tri-Si-Czochralski process wascarried out in collaboration withShell Solar. In the Tri-Siprocess cylindrical Silicium rodsare pulled from the melt, whichconsists of three singlecrystalline columns with almostequal size and having pieshaped cross sections. This Tri-Si structure is assumed to bebeneficial with respect to ahigher mechanical strengthduring sawing and wafering incomparison to monocrystallineSilicium. The Crystal GrowthLaboratory has developedproposals for an optimized hot-zone design of the growthfacility by using numericalsimulation which allows ahigher pulling speed for thesame material quality.

Another cheap method for theproduction of photovoltaicSilicium is the ribbontechnology by using the EFG(Edge-Defined-Film-Fed-Growth)-process. In thistechnique, the shape of thecrystal is defined by a capillarysupplied with Silicium by a meltpool. The multicrystalline crystalis pulled vertically out of the topof the vessel.

The EFG-method utilized at theindustrial partner RWE SchottSolar results in octagonalSilicium tubes (fig. 1) with a wallthickness of some hundred

microns and a length of 5 to 7meters. These tubes are cutinto wafers by a laser cuttingtools. The striking features ofthis process are the lowmaterial losses due to cutting.

Due to technology specificreasons graphite crucibles anddies are usually used in thisEFG-process for photovoltaicSilicium. Graphite has abeneficial wetting behavior withliquid Silicium. This ismandatory for a precise controlof the meniscus and thereforeof the crystal shape. Further ongraphite parts for the crucibleand the die can bemanufactured much easier withclose tolerances especiallycompared to SiO2-glass. The

latter loses considerablymechanical strength at processtemperature.

However, graphite reacts withthe liquid Silicium which leadsto an enrichment of carbon inthe Silicium melt. If the carbonconcentration exceeds thesolubility limit of carbon in liquidSilicium, SiC crystals can formlocally.

The critical concentration is afunction of the temperature.Thus, SiC crystals grow mainlyin the colder regions while inthe hot parts the graphitedissolves. In addition, anenhanced carbon concentrationcan be found in the crystal.

Fig. 1: EFG production facility at RWE-Schott-Solar.

Low cost Siliciumfor photovoltaic applications


This process is governedmainly by to factors: Theefficiency of the carbontransport through the melt fromhot to cold areas and theresistance of the used graphiteagainst the Silicium melt.Up to now only a few resultsexists in the carbon transportduring the Silicium-EFG-process. In some older work thereaction behavior betweenSilicium and different graphitematerials wasphenomenologically analyzed.In addition, a qualitativedescription of the SiC-precipitates as well as firstapproaches for the simulationof the carbon transport in thevicinity of the die exist.However, no quantitativeanalysis of the carbon transportin non isothermal Silicium meltswas carried out.

Therefore, a R&D facility wasinstalled at the Crystal GrowthLaboratory, which allows toperform easily fundamentalexperiments of the dissolutionbehavior of graphite materialsin liquid Silicium.

These experimentalinvestigations are used toobtain a quantitative model forthe carbon transport duringgrowth of Silicium octagons bythe EFG method. For thispurpose a model for thedescription of the diffusive-convective carbon transportwas implemented in thesoftware CrysVUn. Thereby,the carbon dissolution ismodeled by a flux boundarycondition, which containsdissolution rate of the graphitematerial. The R&D activitieswithin this project with RWESchott Solar are focused on a

selection of optimized cruciblematerials and optimizedboundary conditions.

Fig. 2: R&D-facility for the analysis of the reaction behavior between Silicium and

graphite materials.

Chalcopyrite semiconductors forthin film solar cells


Chalcopyrite semiconductorsare promising absorbermaterials for thin film solar cellapplications due to their highabsorption coefficient. The mostimportant compound isCu(In,Ga)Se2 (CIS). InGermany the state of the art inCIS solar cell development isthe installation of two pilotmanufacturing facilities for theproduction of modules withmonolithically integrated cells.

The fabrication of solarmodules by thin film technologyis promising a significantreduction of production costcompared to the Siliciumtechnology dominating themarket today. The material andlabor cost are decreasedbecause of the reducedmaterial usage, the processtechnology simplified byintegrated series connection, aswell as the direct deposition ofthin absorber layers on largeglass or flexible substrates.

Since 1998, Shell solar(formerly Siemens Solar) is thefirst manufacturer ofcommercial CIS solar moduleswith up to 40 W. Whilepresently more than 1 MW ofthis first CIS-module generationhave been tested successfullyon the market, the expansion ofthis technology demandsfurther development in threeareas:

1. Reduction of the productioncost by the higheroperational capacity of in-line manufacturing withmodules larger than 1m²and more than 100 W peakpower compared to thepresent batch processes ofsmaller substrates (<0.5m²).

2. Increased efficiency atmaintained economic life-time.

3. Development of cost-savingalternative processes forfurther reduction of cost ofmaterial and investment.

CGL has been working in thefield of chalcopyrites for solarapplication since the FORSOL(Solar Energy ResearchAssociation) program whichwas established in 1995 withthe support of a number ofinstitutions throughout Europe.

This led to the directcooperation of CGL and Shellsolar, which is currentlyconcentrating on the first twoR&D tasks mentioned above.

At the moment, an extendedcooperation in the third area isplanned.

The main focus of the currentproject, which is supported bythe Bavarian ResearchFoundation, is the optimizationand characterization of the thinfilm deposition and theabsorber formation process. Toachieve a deep insight in theinvolved chemical reactions in-situ methods are applied likeThin Film Calorimetry (TFC), in-situ resistivity measurementsand X-ray- diffraction(cooperation with the Institute ofCrystallography and Structural

Physics, FAU Erlangen-Nürnberg) duringsemiconductor formation.

In the so-called ‘stackedelemental layer’ process usedby Shell solar for the industrialformation of the chalcopyriteabsorber the elementalcomponents of the absorber aredeposited sequentially (in theorder Cu(Ga) → In → Se), andafterwards a Rapid ThermalProcess (RTP) is applied tosynthesize the chalcopyrite.

One topic of research is theincorporation of the Gallium inthe absorber during itsformation. Initially, it wasintended as a means ofwidening the band gap ofCuInSe2 for a better adaptationto the sun spectrum. However,gallium fails to homogenize inthe absorber layer. Itaccumulates at the backcontact of the solar cell, andforms a back surface fieldwhich increases the cellefficiency but does not fullyexploit the efficiency-increasingpotential of homogeneouslydistributed gallium. Below, ourrecent work in this area isdescribed as an example of ouranalysis and optimizationstrategy.

According to our investigations,the inhomogeneous Ga-distribution can be explained by

Fig. 1: Model of the formation of a CIS-absorber during theStacked Elemental Layer process.

M olybdän

C u 2Se + 2 InSe + Se → 2C uInSe 2

C u 2Se + 2(In ,G a)S e + S e → 2C u(In ,G a)S e2

Sele

nIndi

umG

alliu

m

Cu16In9

Se, (Cu,In)

Chalcopyrite semiconductors forthin film solar cells


different reaction kinetics of themetallic absorber componentsCu, In and Ga during thechalcopyrite formation, togetherwith a directional growth of thechalcopyrite layer from the topof the thin film to themolybdenum back electrode(Fig. 1).

Kinetic models (Fig. 2) derivedfrom extensive in-situ analysisof the selenization processsteps show that gallium is muchmore inert to the seleniumattack than e.g. indium:The sequence of the differentphases which progressivelyincorporate selenium during thethermal process is delayed byabout 50 K when comparing Gawith In.

As a result the metallic indiumis already completelyconsumed under these processparameters, while Ga is justbeginning to react. So, galliumis not incorporated in the toplayer selenides but isaccumulating at the bottom ofthe solar cell near the backcontact where it finally forms aGa- rich chalcopyrite layer.

This important insight in themechanism of absorberformation should allow foroptimization strategies – eitherby altering the depositionprocess or the thermaltreatment of the absorber –resulting in a morehomogeneous Ga-depth profileand subsequently higherefficiencies of the industrialsolar cells.

Recent PublicationsA. Brummer, V. Honkimäki, P.Berwian, V. Probst, J. Palm, R.Hock, Thin Solid Films 437(2003) 297-307

P. Berwian, A. Weimar, G.Müller, Thin Solid Films 431-432 (2003) 41-45

Ch. Hack, D. Seng, P.Wellmann, G. Müller, E-MRSSpring Meeting 2002,Strasbourg

J. Auer, Ch. Hack, P. Berwian,G. Müller, E-MRS SpringMeeting 2002, Strasbourg

P. Berwian, J. Hirmke, A.Brummer, G. Müller, 13thInternational Conference onTernary and MultinaryCompounds, Paris, 2002

Ch. Hack, J. Auer, S. Hussy, G.Müller, 13th InternationalConference on Ternary andMultinary Compounds, Paris,2002

0%

25%

50%

75%

100%

200 250 300 350 400 450Temperatur [°C]

Kon

zent

ratio

n

In+SeIn4Se3InSeIn2Se3Ga+SeGaSe

Fig. 2: Modelled phase content of In-Se and Ga-Se thin films during rapidthermal processing.


contact [email protected]

The increasing requirement onthe quality and productivity ofcrystal growth processesmakes it necessary to optimizethe processing by acombination of experimentalknowledge and computermodeling.

For this purpose the CrystalGrowth Laboratory developssimulation programs whichallows the user to analyze andoptimize the crystal growthprocess. CrysVUn is anindustrial approved, userfriendly simulation softwarewhich enables researchers thein deep investigation of hightemperature furnaces in twodimensions.

The ongoing increase ofcomputer performance makes itnow possible to establish threedimensional simulation softwarealso on low cost PC hardwarewhat is used in mostcompanies. CrysVUn3D isaimed to fulfill this logical nextstep toward a global simulationof high temperature processesin three dimensional geometrieswhile keeping up the user-friendliness.

When starting a large scalesoftware project with a run-timeover years involving a couple ofman-years one is forced tostructure the software in a waythat it remains maintainable andmanageable. The complexity ofthe application makes itinevitable to use approvedsoftware packages taking oversubtask. The software structuremust allow the easyreplacement of these packageswhen another software packageexhibits better properties.

The software design ofCrysVUn3D targets on these

requirements. The basic idea isto build up the basic system ofthe software from elementarycomponents. The componentsare very compact, all that isknown about them is what typeof object they represent - e. g. avolumetric mesh, a matrix.

The components provide theirfunctionality via a collection ofinterfaces. An interface itselfprovides a set of semanticallyrelated methods. The entirety ofall interfaces of a componentbuild up the actual functionalityof that component. With thisconcept a component is a veryabstract term in the softwarearchitecture without any majorimplementation.

A realization of a component isthe polymorphic derivation ofthe component and it is meantto implement all of theassociated interfaces. Typically,component realizations requiresthe implementation of more

than one interface but not all ofits interfaces (Figure 1).The application cannot accessthe realization directly. Insteadit has to use the abstractcomponent interface whichinternally points to the actualimplementation. The decouplingof usage and realizationprovides a set of advantages.

A major benefit of the design isthat the realization of thecomponent need not to belinked to the application. It willbe connected dynamically notuntil it is needed by theapplication. This implies thatporting the application to aspecialized hardware, i.e. highperformance computers, resultsin porting only those componentrealizations which are requiredby the application to performthe task. There may also existdifferent implementations of thesame component and theapplication can switch betweenthem even at runtime. Theintegration and replacement of

Figure 1: The CrysVUn3D software architecture is based on acomponent model with interchangeable implementations.


contact [email protected]

commercial-off-the-shelflibraries and products canefficiently be done viaadaptation of the libraryinterface to the componentinterface. The introduction ofstrict interfaces prevents theapplication developer as user ofthe components from writinghighly inter-depended softwaremodules. This results in anincrease of maintainability andmanageability of the softwareproject.

Exchanging components atapplication runtime requiresthat all information about acomponent that would havebeen accessible when theapplication was compiled, mustnow be able to be queried atruntime. This can be achievedby adding reflexivity to thecomponent. Such componentscan give information about whatcan be done with them andabout what data they contain.With the help of reflexivecomponents the application canbe designed in a generic, butyet efficient way. An examplefor this is the automized user-interface generation.

A reflexive component can bequeried about its inputparameters and about theirtype. This information is used togenerate a GUI (Graphical UserInterface) of a component withthe help of some GUI-Toolkit,like wxWindows. Using adescription file per component,additional attributes of the GUIcan be set up. We are using adescription in XML syntax(eXtensible Markup Language)for specifying - among othertasks - the global layout of allelements and the labeling andthe look of each element.Furthermore the XMLdescription may contain rules

that link elements with eachother. For example rules like: "ifelement A is active, thenelement B is enabled, elseelement B is disabled", may bespecified. By using the XMLdescription file the user-interface can be rapidlyadapted to the needs of anapplication without the need torecompile a component. Figure2 illustrates the process of anautomized user-interfacegeneration from the mainapplication's point of view.

With this software design webuilt up a base system for asimulation program which caneasily be extent by newmodules. The introduction ofcomponents with thereinterfaces ensures a welldefined behavior of the module.This module concept allowsalso to write extensions which

connects the application withother programs.

The component implementationmay reside on the localcomputer or can be distributedover the network. The networkcommunication is encapsulatedby the base system and iscompletely transparent for theuser of the component.The automatic generation of theGUI for setting the parametersof the component by the userreduces the cost ofdevelopment as well as itavoids that the in-deep-knowledge of the moduledeveloper about the underlingwindow system is neededwhich may vary betweendifferent platforms.

Figure 2: At runtime the main application loads componentsand generates the user-interface for the input parameters ofthe component. The user-interface details are specified in a

XML description file that accompanies the component.



The growth of bulksemiconductor crystals from themelt requires the control ofstrictly defined temperaturefields in the melt and in thegrowing crystal. Partially,conflicting demands are madeon these temperature fields. Forexample, a high axialtemperature gradient isrequired for an exact definitionof the solid-liquid interfaceposition at a given growthstage. On the other hand, thisleads to an increase of thethermoelastic stresses andconsequently to an amplifiedformation of defects in thecrystal.

An optimal control of thetemperature filed is onlypossible if the process, i.e. thetime-dependent settings ofheater powers, and the designof the furnace are adapted toeach other.

For years now, numericalsimulation is a standard tool forthe development of newequipment and processes.

Typically, one builds anempirically based model of afurnace which is then used todevelop a suitable growthprocess by manual variation ofparameters. An automization ofthis time-consuming andexpensive developmentprocess requires aparameterization as well ofparts of the equipment as of theprocess itself. However, thenumber of necessaryparameters growths rapidly,making a complete screeningof the search space spanned bythese parameters impossible.Therefore, the application ofoptimization methods becomesinevitable. As there are typicallyno smooth transitions from

different processes to matchingfurnaces, this search space isstrongly nonlinear and not wellsuited for classical optimizationalgorithms based e.g. on thesearch of the steepest descend.

In the field of crystal growth,CrysVUn, developed at CGL,has been one of the firstcommercial software toolsincluding optimizationstrategies. By the so-calledinverse simulation it waspossible for a given furnacegeometry to automaticallycompute heater

powers and temperaturesrequired to obtain a desiredtemperature distribution. Theuse of soft-computingapproaches can be consideredas a further development of thisoptimization strategy. The term„soft-computing“ comprisesmethods like fuzzy logic, neuralcomputing, probabilisticreasoning and evolutionarycomputing. While abandoningto a certain degree proofs ofcompleteness and exactness,these approaches make itfeasible to treat and solve

Fig.1: Optimization of the material distribution and the thermal processingfor a model facility for the VGF-growth of GaAs crystals by using geneticalgorithms and CrysVUn. Left: initial configuration, thermal stress in thecrystal 2.8Mpa, right optimized material distribution, stress in the crystal

0.7MPa



complex and otherwiseimpossible to problems.

As a first example, theapplicability of geneticalgorithms in conjunction withthe thermal modeling toolCrysVUn has been.

Genetic algorithms encodegiven sets of parameters into bitstrings, so-called individuals. Agroup of these individuals formsa population. The „fitness“ ofeach individual is evaluated bymeans of the „fitness-function“.In the present case, this meansthe conduction of a thermalsimulation using the parametersgiven by each individual.Following the biologicalparadigm, individuals within apopulation compete then,based on their fitness. Afterevaluation of each generation,different recombination- andmutation operators are appliedand a new generation is built.

The applicability of geneticalgorithms could be shown fortwo industrially relevant crystalgrowth processes: The growthof GaAs using the verticalgradient freeze (VGF) process,and the growth of Silicium bythe Czochralski-method.For the case of growth GaAs,the distribution of insulationmaterials inside a modelfurnace has been optimizedtogether with the settings for 6heating elements. 28 freeparameters where subject tooptimization, the fitnessfunction was composed from 13partially conflicting demands.Using 13 CPU's (AMD 1600+)in parallel, a result fulfilling allrequirements could be obtainedwithin 4 days.

Currently, in a cooperation withCrystal Growing Systems

GmbH, Hanau (CGS), theinner assembly for a industrial

new VGF-furnace for thegrowth of 6“ GaAs is beingdeveloped.

As a second test case, thegeometry of heat shields aswell as the position of the sideheater inside a Czochralski-Furnace for the growth ofSilicium has been optimized.The goal of the optimizationwas to maximize, at a givengrowth rate, the axialtemperature gradient inside the

crystal. The main constraint inthis case was a maximum

temperature in the melt toprevent crucible degradation.Also for this example it could beshown that, using a PC cluster,good results can be obtainedwithin some days. Compared tothis, our experience shows thatsuch optimizations, manuallyvarying parameters by trial anderror, take typically severalweeks.

Fig.2: Optimization of heat shields in a Silicium-Czochralski-puller: leftInitial configuration, right optimized result

Modeling of melt convectionby 2D – 3D coupling


It is well known that convectiveheat transfer in thesemiconductor and oxide meltshas a strong influence on forexample the axial temperaturegradient in the crystal, theshape of the solid-liquidinterface or on the transport ofspecies.

Therefore, three-dimensionalmodels are more often took toanalyze the influence ofdifferent process parameters onmelt convection.

Widely spread is the use ofpartial 3-D models, whichtypically consist of crucible,melt and crystal (see Fig. 1).Mainly fixed temperatures (orsometimes heat fluxes) areimposed at the boundaries ofthe computational domain.These boundary conditions aretaken either from global 2-Dsimulations or frommeasurements. The crystal-melt isotherm has either a fixedshape or in the more advancedcase is treated as a Stephancondition with a given growthrate.

The melt flow is calculated bysolving the 3-D time-dependentequations of mass, momentumand heat conservation takinginto account the Boussinesqapproximation for anincompressible Newtonian fluid.The models are based either on(quasi) Direct NumericalSimulation or take into accountturbulence models like the lowReynolds-k-ε or Large Eddy.

A typical example for such amodel is the commercialsoftware programSTHAMAS3D, which issuccessfully used for the studyof Cz Si and LEC - GaAs under

the action of various magneticfields.

3-D time-dependent simulationsof Si Czochralski configurationswere carried out by usingSTHAMAS3D to analyze theinfluence of various growthparameters and magnetic fieldsincluding EMCz. The resultswere also compared toexperimental data. It turns outthat the overall temperaturedistributions are in betteragreement with experimentsthan those of 2-D simulations,although the mesh size iscoarse (3 105–106 cells) andsolutions are not fully grid

independent. However, themost critical validation ofmodeling is the quantitativecomparison of the Fourieranalysis of calculatedtemperature fluctuations tomeasured ones. In this case,the best results were achievedby a numerical technique whichuses a “flux blending” instead ofthe usual approaches, likelarge-eddy-simulation andReynolds-averaged turbulencemodels.

It was clearly demonstrated thatthe Reynolds averaged methodusing k-ε model fails to predictthe temperature fluctuations.

Figure 1. Temperature distribution in LEC-GaAs melt(top)and Si-Cz melt (bottom).

Modeling of melt convectionby 2D – 3D coupling


Recent results of acollaboration of CGL withFreiberger Compound Materialson the LEC growth of GaAsprove that a 3-D modeling isuseful to predict the shape ofthe solid-liquid interface underthe influence of various growthparameters. It turns out thattemperature fluctuations have astrong influence on theinterface shape.

Although the strategy ofperforming local 3-Dsimulations with proper thermalboundary conditions obtainedfrom global 2-D-simulationsresults in a better agreementthan the pure 2-D approach, areal coupling between global 2-D- and local 3-D-simulations isnecessary, because the meltconvection influences thethermal field not only locally inthe melt. The convective heattransport in the melt mightrequire that the heating powerin the 2-D-simulations has to beadapted to the new conditions.This would again result in newboundary conditions for the 3-D-simulations.

In order to meet this challenge,CGL put many efforts in thecoupling of STHAMAS3D withthe other 2D global modelingtools STHAMAS and CrysVUn.

In a first step it was analyzedwhich kind of boundaryconditions (heat flux or fixedtemperature) should betransferred from the global 2Dsimulations and how sensitivethe 3D results are to smallchanges in the thermalboundary conditions.

It turned out that especially fora more realistic coupled 3Dmodel of the LEC growth ofGaAs the type of boundary

conditions (i.e. heat fluxes,fixed temperatures or acombination of both) is veryimportant. A change of theabsolute temperature along thecrucible wall by 1 or 2K cansignificantly change theconvective heat transport andtherefore the shape of the solid-liquid interface. On the otherhand, the position where theseboundary conditions are applied(i.e. e.g. at the inner or outer

crucible wall) seems to be lessimportant.

It is clear that three-dimensionaltime-dependent melt flow has agreat influence on the globalheat exchange so that thetransfer of the information fromthe 3D local simulation to the2D global simulation should beconsidered. This back-couplingwill be considered in the futuredevelopments of STHAMAS3D.

Figure 2: Temperature profiles along the inner crucible wall for a GaAs-LEC melt obtained from STHAMAS3D simulations for the three different

types of boundary conditions:

Case A) fixed temperature at the inner crucible wall and at the meltsurface;

Case B) fixed heat flux at the inner crucible wall and at the melt surface;

Case C) fixed heat flux at the outer crucible wall and at the melt surface.



Structural defects, likedislocations have a bigimportance for the applicationof semiconductor crystals assubstrates for the devicemanufacturing. In many casesthese dislocations havenegative effects on the qualityof the manufactured devices.One of the main causes togenerate dislocations is theplastic deformation of thecrystal as an effect of stress.During the growth process ofthe crystal from the melt or fromthe gas phase thermoelasticstress is generated as a resultof the inhomogeneoustemperature field in the growingcrystal. This can cause thegeneration and the movementof dislocations. During thecrystal growing process, theagglomerations of dislocationscan induce the formation ofgrain boundaries and this canreduce the yield. This is a bigproblem particularly growingsemiconductors like Gallium-Arsenid and Indium-Phosphide.Also in the case of SiliciumCzochralski growth dislocationsare getting more and moreimportant.

As a result of the mentionedproblems the Crystal GrowthLaboratory develops anumerical model to describe thedislocation dynamics during thegrowth of semiconductors andoptic crystals in the frameworkof a research fellowship of the“Förderkreis für Mikroelektronike.V.” After the verification of themodel with experimental data,the model will be used toanalyze the influence ofdifferent process parameters onthe formation and on thedistribution of dislocations in thecrystal.

The dynamics of thedislocations is a physicallyextremely complex process.Thus, the development and theverification of the dislocationmodel takes place step-wise. Inorder to get from a qualitativedescription of this problem to aquantitative one additionalphysical effects will be addedstep-by-step. With this iterativeprocedure it is possible at everystep of this development toperform a parameter study withthe corresponding model.

The first assumption for thedevelopment of the dislocationmodel is the possibility tocalculate the thermal stressconsidering the plasticdeformation. In the first step theelastic stress model alreadyavailable in the software packetCrysVUn is extended takinginto account the plasticdeformation.

To describe the dependencybetween plastic deformation inthe crystal and the motion ofthe dislocation the classicalAlexander-Haasen model (AH-model) is used. First, theimplementation of the AH-model is done in theaxisymmetric quasistationaryapproximation.

For specific physical conditions,for example constant effectivestress, the equations of the AH-model are analyticallyresolvable. With this analyticalsolutions the implemented AH-model was verified for specifictest cases.

In addition first test results areavailable for the verification ofthe implemented model withpublished data. The outcomeon this is a good agreementbetween the published results

With CrysVUn computedvon Mises stress

(top, max. 1.2 MPa),dislocation density

(middle; 1000 cm-2) andresulting residual stress (bottom, max. 0.8MPa)

in a GaAs-crystal with 2cmdiameter and a axial temperature

gradient of 7K/cm.



and the calculated dislocationdensity with the implementedAH-model.

The quasistationaryapproximation of the availableAH-model gives informationabout the dislocation dynamicduring the crystal growthprocess, not during the coolingprocess or during thesubsequent annealing steps.Therefore the existing modelwill be extended in the nextstep, to be able to calculatetime-dependent phenomena.

The dislocation dynamic is inreality a three dimensionalprocess, in which each slipplane and slip direction hasimportance. Therefore in thethird development phase themodel will be extended to beable to calculate the dislocationdensity in each slip plane. Thesum of the density from eachslip plane gives then the densityof the dislocations in the wholecrystal. Such calculations areonly possible in the threedimensional description of thecrystal.

Thus, a 3D program for stresscalculations was developed andverified, in which the dislocationmodel will be implemented.

Parallel to the development ofthe model the study of theeffect of the growth condition onthe dynamic of the dislocationsfor the growth of III-Vsemiconductors and opticalcrystals are continued.

Distribution of the von Mises stress in a 8“ GaAs crystal for atemperature gradient of 10K/cm:

Benchmark solution from Ansys (top); Solution with own 3Dprogram (bottom)

The virtual Material Science Laboratoryonboard the International Space Station


Experimental research in amicrogravity environment hasnow a long tradition in the fieldof material science. Theabsence of gravity helps tocreate defined conditions forthe occurring heat and masstransfer during solidificationprocesses. This allows tovalidate theoretical models andto develop fundamentalrelations between solidificationconditions and the resultingmaterial properties.

The planned Material ScienceLaboratory (MSL) of theEuropean Space Agency (ESA)onboard the InternationalSpace Station (ISS) shallenable the long term access toa microgravity environmentduring the next 10-15 years.MSL consists primarily of aprocess chamberaccommodating furnace insertsand individual experimentcartridges (see figure 1). So far,the Low Gradient Furnace(LGF) and the Solidification andQuenching Furnace (SQF) areplanned to be the firstEuropean furnace inserts in theMSL. Both, LGF and SQF areBridgman-type furnaces, inwhich the cartridge containingthe sample is moving relative tothe furnace insert during theexperiments. A fundamentalfeature of MSL is its capabilityfor on-orbit exchange of furnaceinserts. In this way, the facilitysupports various materialsprocessing techniques withdifferent thermal profiles. Thisgives researchers the possibilityto design new furnace insertsas scientific requirementsevolve. Thereby, the foreseenexperiments consider a widerange of material systems, like,e.g., AlSiMg, CdTe and CuSn.

In the framework of the MaterialScience Laboratory UserSupport Program ESA hascommissioned the CGL todevelop a “virtual” materialscience laboratory, based onthe CrysVUn software, whichwas developed at CGL in thelast years. CrysVUn isespecially designed for globalsimulation of heat and masstransport processes in hightemperature furnaces withcomplex axi-symmetric or 2Dgeometries.

The virtual material sciencelaboratory shall be used forthermal simulations of thesolidification and crystal growthexperiments in order to support,e.g.,• the cartridge development,

in such way that a proper

thermal set-up of thesample cartridge systemcan be identified, which fitsto the dedicated scientificrequirements.

• the preparation andexecution of flightexperiments, as well as theground based referenceexperiments. The goal is todefine and optimize theprocess parameters, e.g.,temporal evolution of heatertemperatures or thetranslation velocity of thefurnace, in order to achievea certain thermal field insidethe sample.

• the experimentalists fortheir further scientificevaluation by providingdetailed information aboutthe thermal field inside thesample-cartridge assembly

Fig. 1: Schematic of the Material Science Laboratory (source: ESA). Thefurnace insert and sample-cartridge assemblies are exchangeable duringon-orbit processing. Numerical modeling of these parts with the software

package CrysVUn helps to define proper thermal set-ups and optimalprocess conditions.

The virtual Material Science Laboratoryonboard the International Space Station


during the flightexperiments as well asduring the referenceexperiments on ground (seefigure 2).

To fulfill all this requirements,CrysVUn was extended duringthe last year with several newfeatures, like a comfortablematerial data base. Currently,the developed thermal modelsare validated with experimentalmeasurements of thetemperature distribution insidethe furnaces. Thereby, weapply the recently developedgenetic algorithms (GA) for thesystematic parameter variationof some critical materialproperties. One particulardifficulty is the identification ofthe effective thermalconductivity of the heat shieldsused in the furnace inserts.

It can be expected, thatCrysVUn will be usedextensively by CGL and otherEuropean research groups forthe support of experiments inthe field of material scienceonboard the ISS. Nevertheless,as the MSL will not be availablein the near future, the Europeanresearches have to utilizealternative flight opportunities,like sounding rocket missions.As an example, CrysVUn iscurrently applied to support andanalyze an experiment onboardthe TEXUS41 missionscheduled for November 292004. This rocket flight is part ofthe European research programMICAST in which CGL isinvolved. The goal of thisproject is to analyze theinfluence of electromagneticallydriven flows on themicrostructure development ofAlSi alloys.

Recent PublicationsJ. Friedrich, J. Dagner, M.Hainke, G. Müller, Crys. Res.Technol. 38, No.7-8, 726-733,2003.

M. Hainke, J. Friedrich, G.Müller, Elgra News 23, 103,2003.

J. Dagner; M. Hainke, J.Friedrich, G. Müller,

Proc. of 4th Int. Conf.Electromagnetic Processing ofMaterials, Lyon, A2 3.6, 2003.

M. Hainke, J. Dagner, J.Friedrich, G. Müller, 17thThermal and ECLS Softwareworkshop, ESTEC, 2003.

Fig. 2: Performance of a solidification experiment in the virtual materialscience laboratory. The thermal analysis with CrysVUn provides

detailed information on the temperature field inside the furnace insertand the sample-cartridge assembly.

Staff

Name Tel. +49-9131- Email

Rainer Apelt

Dr. Gheorghe Ardelean

Noemi Banos

Patrick Berwian

Dr. Bernhard Birkmann

Isabel Brauer

Johannes Dagner

Elke Dutzel

Dr. Jakob Fainberg

Dr. Jochen Friedrich

Tim Fühner

Oliver Gräbner

Horst Hadler

Marc Hainke

Elisabeth Henneberger

Stephan Hussy

Jiri Janeba

Dr. Thomas Jung

Flaviu Jurma

Michael Kellner

Lothar Kowalski

Bernd Kreß

Dr. Elke Meissner

Alexander Molchanov

Prof. Dr. Georg Müller

Michael Purwins

Uwe Sahr

Peter Schwesig

Paul Sonda

Guoli Sun

Dr. Daniel Vizman

761-252

761-265

761-229

852-7757

761-136

752-8613

761-266

761-270

761-231

761-344

761-261

761-226

761-273

761-233

852-7729

761-251

761-233

761-264

761-135

761-273

852-7720

85-27722

761-136

761-225

852-7636

852-7757

852-7722

852-7722

761-272

761-135

761-229

[email protected]

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Publications

2003

A. Brummer, V. Honkimäki, P. Berwian, V. Probst, J. Palm and R. HockFormation of CuInSe2 by the annealing of stacked elemental layers––analysis by in situ high-energypowder diffractionThin Solid Films, Volume 437, Issues 1-2, 1 August 2003, Pages 297-307

P. Berwian, A. Weimar and G. MuellerIn situ resistivity measurements of precursor reactions in the Cu–In–Ga systemThin Solid Films, Volumes 431-432, 1 May 2003, Pages 41-45

O. Czarny, P. Droll, M. Ganaaoui, B. Fischer, M. Hainke, M. Metzger, G. Müller et al.High performance computer codes and their application to optimize crystal growth processes IIIin E. H. Hirschel (ed.): Numerical Flow Simulation III, CNRS-DFG Collaborative ResearchProgramme Results 2000-2002, Springer-Verlag, Berlin (2003) 49-76

J. Dagner, M. Hainke, J. Friedrich, G. MuellerEffects of time-dependent magnetic fields on directional solidification of AlSi7 alloys4th Int. Conf. on Electromagnetic Processing of Materials, EPM200314-17 October 2003, Lyon, France, A2 3.6, 2003

J. Friedrich, J. Dagner, M. Hainke, G. MuellerNumerical modelign of crystal growth and solidification experiments carried out under mcirogravityconditionsCryst. Res. Technol. 38 (2003) 726-733

M. Hainke, J. Friedrich, G. MuellerNumerical Study of the Effects of Rotating Magnetic Fields during the VGF Growth of 3'' GaAsCrystalsMag. Hyd., Vol. 39, No. 4 (2003) pp. 515-522

M. Hainke, J. Friedrich, D. Vizman, G. MuellerMHD Effects in semiconductor crystal growth and alloy solidificationProc. of Int. Scientific Colloquium on Modelling for Electromagnetic Processing (Eds. B. Naacke, E.Baake) 2003 73-78

M. Krause, J. Friedrich, G. MuellerSystematic study of the influence of the Czochralski hot zone design on the point defect distributionwith respect to a perfect crystalMaterial Science in Semiconductor Processing 5 (2003) 361-367

A. Molchanov, O. Graebner, G. Wehrhan, J. Friedrich, G. MuellerOptimization of the growth of CaF2 crystals by model experiments and numerical simulationJournal of the Korean Crystal Growth and Technology 13 (2003) 15-18

G. MuellerModeling of crystal growth from the meltin Computational Modelling and Simulations of Materials (eds. P. Vincenzini, A. Lami) 2003 TechnaSrl. 267-278

V. Socoliuc, D. Vizman, B. Fischer, J. Friedrich, G. Mueller3D numerical simulation of Rayleigh-Bėnard convection in an electrically conducting melt acted onby a travelling magnetic fieldMagnetohydrodynamics 39, 2 (2003) 187-200

Publications

2002

B. Birkmann, R. Weingaertner, P. Wellmann, B. Wiedemann, G. MuellerAnalysis of silicon incorporation into VGF-grown GaAsJ. Crystal Growth 237-239 (2002) 345-349

J. Friedrich, R. Backofen, G. MuellerNumerical simulation of grain structure and global heat transport during solidification of technicalalloys in MSL inserts under diffusive conditionsAdv. Space Res. 29/4 (2002) 549-552

I. R. Grant, U. Sahr, G. MuellerGrowth of InP and GaAs Substrate Crystals by the Vertical Gradient Freeze MethodConf. Proc., 14th International Conference on Indium Phosphide and Related Materials (2002) 413-415

M. Hainke, J. Friedrich, G. MuellerNumerical Study of the Effects of Rotating Magnetic Fields during VGF Growth of 3" GaAs CrystalsProc. of 5th Int. Pamir Conference (2002) V-1

A. Molchanov, U. Hilburger, J. Friedrich, M. Finkbeiner, G. Wehrhan, G. MuellerExperimental verification of the numerical model for a CaF2 crystal growth processCrystal Reseach and Technology 37 (2002), 77-82

G. Mueller, B. Birkmann,Optimization of VGF-growth of GaAs crystals by the aid of numerical modelling,J. Crystal Growth, 237-239 (2002) 1745-1751

G. MuellerExperimental analysis and modeling of melt growth processesJ. Crystal Growth 237-239 (2002)1628-1637

G. Mueller, O. Graebner, D. VizmanSimulation of crystal pulling and comparison to experimental analysis of the CZ-processin Semiconductor Silicon 2002 (eds. H.R. Hunt, L. Fabry, S. Kishino) Electrochemical Society (2002)489-504

O. Paetzold, B. Fischer, A. CroellMelt flow and species transport in µg-gradient freeze growth of GermaniumCryst. Res. Technol. 37 (2002) 1058-1065

Y. Stry, M. Hainke, T. JungComaprison of linear and quadratic shape functions for a hybrid control-volume finite elementmethodInt. Journal of Numerical Methods for Heat&Fluid Flow, Vol. 12(8) (2002) 1009-1031

U. Sahr, G. MüllerGrowth of InP Substrate Crystals by the Vertical Gradient Freeze TechniqueConf. Proc., 12th Semiconducting and Insulating Materials Conference (2002)

D. Vizman, O. Graebner, G. Mueller3D numerical simulation and experimental investigations of melt flow in a Si Czochralski melt underthe influence of a cusp-magnetic fieldJournal of Crystal Growth 236(4) (2002) pp. 545-550

Equipment

http://www.kristallabor.de

Laboratory space200 m2 laboratory space in total at university and Fraunhofer IISB plus offices

Crystal growth• several multi-zone furnaces for vacuum and high pressure conditions (for 2" - 6" crystal

diameter)• several multi zone furnaces for sample preparation and growth of small diameter crystals• 1 liquid phase epitaxy facility

Analysis and characterization of materials• Several optical/infrared microscopes• Access to high resolution microscopes• Mapping system for optical spectroscopy of semiconductor wafers• Interferometric profilometer for surface analysis of semiconductor wafers• X-ray Laue camera• Hall-measurement-system (temperature dependent 15K-650K)• Measurement system for characterization of deep and shallow levels by capacitance techniques

(CV, DLTS) and by conductance techniques (TSC, PICTS)• Photoluminescence system (14K and 300K), IR-absorption, both systems suitable for mapping• Differential Thermal Analysis for determination of phase diagrams• Differential Scanning Calorimeter for thermodynamic and kinetic studies• Thermogravimetry

Preparation and metallography• Facilities for preparative work related to wafer preparation (grinder, annular and wire saws,

lapping and polishing equipment)• Several evaporation systems• Sputtering systems (DC, 6" target diameter)

Contact and travel information

ContactCrystal Growth Laboratory Crystal Growth LaboratoryProf. Dr. Georg Müller Dr. Jochen FriedrichUniversity Erlangen-Nürnberg Fraunhofer IISBMartensstrasse 7 Schottkystrasse 1091058 Erlangen 91058 ErlangenPhone: +49-9131-852-7636 Phone: +49-9131-761-269Fax: + 49-9131-852-8495 Fax: + 49-9131-761-280http://www.kristallabor.de http://www.kristallabor.deEmail: [email protected] Email: [email protected]

Travel Information

By carUse Autobahn A3, exit Tennenlohe, followsigns for Erlangen, after 2 km take exit for"Universität Südgelände", then follow signsfor IISB: 1.6 km north on Kurt-Schumacher-Straße, then turn left twice into Cauerstraßeand Schottkystraße.

By planeFrom Nürnberg (Nuremberg) airport use taxi(15 minutes) or bus 32 to Nürnberg-Thonand then bus 30/30E to Erlangen-Süd (30minutes).

By trainFrom Erlangen station, use taxi (15 minutes)or bus 287 to Stettiner Straße (30 minutes).Convenient train services from NürnbergHauptbahnhof (central station) to Erlangenstation.

Tourist InformationVerkehrsverein Erlangen e.V.Rathausplatz 1, 91052 Erlangen, GermanyPhone:+49-9131 89-150Fax: +49-9131 89-5151WWW:www.erlangen.de

crystal growth laboratory · soft-computing in crystal growth modeling of melt convection by 2d –...

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