ERBIUMDOPEDIII-N MATERIALSFORNEAR-IROPTOELECTRONICS By DEVINMACKENZIE J. ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT OFTHEREQUIREMENTSFORTHEDEGREEOF DOCTOROFPHILOSOPHY UNIVERSITYOFFLORIDA 1998 ACKNOWLEDGMENTS TheauthorowesanincredibledebttoProf.CammyR.Abernathy. Withouthersupport fromthefirstdayofgraduateschooltothelast,thiscouldnothavebeenpossible. Eveninthe mostdifficulttimes,thevalueoftheacademicandpersonalrelationshipwithherwasundeni- able. TheauthorisalsoindebtedtoProfKirkKolenbranderandProfRezaAbbaschianfor leadinghimtoCammysdoor. Inthefuture,theauthorcouldnothopetoworkwithsomeone morecapable,understandingoruncannilyreasonablethanProfAbernathy.Thanks. Manythanksarealsoduetothemanycollaboratorswhohavecontributedtothiswork including:ProfStephenPearton,Dr.UweHommerichandhisgroup,ProfFanRen,Dr.Rob- ertWilson,Dr.RobertSchwartz,Dr.JohnZavada,Dr.PaulChen,ProfLenBrillsonandhis group,SeanDonovan,CraigSchardtandW.Krishnamoorthy. 11 TABLEOF CONTENTS ACKNOWLEDGMENTS i ABSTRACT v CHAPTERS 1 INTRODUCTION: NEARIRTECHNOLOGIES ANDTHEIII-N SEMICONDUCTORS 1 2 GROUPIII-NGROWTHBYPLASMA-ASSISTEDMETALORGANIC MOLECULARBEAMEPITAXY 12 2.1 ABriefHistoryofIII-NResearch 12 2.2MetalorganicMolecularBeamEpitaxyofIII-NSemiconductors 13 2.3TheMetalorganicMolecularBeamEpitaxyGrowthSystem 17 2.4VaccuumSystems 24 2.5GeneralGrowthProcedures 27 2.6Characterization 30 3 OPTIMIZATIONOFIII-NGROWTHBYPLASMA-ASSISTED METALORGANICMOLECULARBEAMEPITAXY 34 3.1 AnOptimizationStudyofMetalorganicMolecularBeamEpitaxyofAluminum NitrideandGalliumNitrideSemiconductors 34 3.2AlternativeOxideSubstratesforIII-NHeteroepitaxy 47 3.3PlasmaCharacteristicsandtheGrowthofGroupIll-NitridesbyMetalorganic MolecularBeamEpitaxy 54 4ALUMINUMNITRIDEDOPEDWITHERBIUMDURINGGROWTHBY PLASMA-ASSISTEDMETALORGANICMOLECULARBEAMEPITAXY 67 5 GROWTHANDLUMINESCENCEPROPERTIESOFGALLIUMNITRIDE DOPEDWITHERBIUMDURINGDEPOSITIONBYPLASMA-ASSISTED METALORGANICMOLECULARBEAMEPITAXY 78 iii 6 OPTICALANDELECTRICALEXCITATIONOFMETALORGANIC MOLECULARBEAMEPITAXY-DERIVEDGaN:ErSTRUCTURES INTEGRATEDWITHSILICON 90 REFERENCES 109 BIOGRAPHICALSKETCH 115 IV AbstractofDissertationPresentedtotheGraduateSchool oftheUniversityofFloridainPartialFulfillmentofthe RequirementsfortheDegreeofDoctorofPhilosophy ERBIUMDOPINGOFIII-NMATERIALSFORNEAR-IROPTOELECTRONICS By J.DevinMacKenzie August1998 Chairman:ProfessorCammyR.Abernathy MajorDepartment:MaterialsScienceandEngineering Inthisdissertation,thepotentialforIII-N:Ermaterials,epitaxially-growninultrahigh vacuum,asabasisfornear-IRoptoelectronicdevicesintegratedwithSihasbeendemonstrated. Thisresearcheffort’sscopeincludesthedevelopmentandunderstandingofIII-Nmatrixgrowth fromchemicalbeamsinultrahighvacuum,thedemonstrationandstudyoftheincorporation andluminescencebehaviorofErinIII-Nmaterials,andfinally,therealizationofelectrolumines- centGaN:Erstructuresemittingat1.54pm. Exploitationofthe1.54pmintra-4fshelltransi- tionoftheEr3*ionisofimmediatetechnologicalsignificanceasthisradiativetransitionmatches theattenuationlossminimaofsilicafibers.AIII-Ndevice,utilizingErasanopticalcenterand compatiblewitheconomically-developedSitechnology,couldprovideanefficient,temperature stable,andinexpensivelightsourceforfibercommunicationssystemsaswellasforhighspeed opticalinterconnectsatalllevelsofcomputerintegration.Metalorganicmolecularbeamepitaxy (MOMBE),thegrowthtechniqueusedinthiswork,wasideallysuitedforthisresearchasit allowedforgrowthfromelementalbeams,metalorganicprecursors,andradio-frequency(RF) andelectroncyclotronresonance(ECR)plasmasoverarangeofoperatingconditions.Also,the MOMBEapparatusprovidesthecapabilitytotailordeviceandmaterialsparameterssuchasrare- earthandelectricaldopantprofilesandimpuritylevels. Highquality,GaNandAINfilmsweregrownepitaxiallyon(0001)A1203. Optimized growthconditionsweredeterminedforgrowthofIII-NmaterialsfromECRandRFnitrogen plasmas. ControloverimpuritybackgroundsthroughtheuseofvariousGroupIIIsourceswas achieved.Plasmaparameterswerecorrelatedwithfilmcharacteristicsandopticalemissionspec- traofthe RFandECRplasmastodeducetheoptimalGroupVconditionsforgrowth. Solid sourcedopingandmetalorganicsourceswereutilizedtointroduceErintoIII-Nfilms during growth. Forthefirsttime,strong,room-temperature1.54pmphotoluminescence(PL)was observedfromAIN,InN,GaN andInAINdopedwithErduringgrowth. Devicestructures fabricatedfromMOMBE-derivedGaN:Erdemonstrated,forthefirsttime,electrolumines- cenceatroomtemperaturefromIII-N:ErmaterialsintegratedwithSi.Also,forthefirsttime, electroluminescencehasbeenobservedfromInAIN:Er-basedSchottkystructuresonSi.Lumi- nescence,growthandimplantationexperimentswereperformedtodeducetheinteractionbe- tweenopticallyactiveErandcarbonandoxygen.Anacceptor-likeenergy-transferstatemodel associatedwithChasbeenproposedtoexplaintheopticalactivationofErinMOMBE-derived GaN. vi CHAPTER 1 INTRODUCTION: NEARIRTECHNOLOGIES ANDTHEIII-NSEMICONDUCTORS Therevolutionaryimpactofmicroelectronicsinthesecondhalfofthiscenturycanbeseen ateverylevelofmodernsociety.Fromtheoutset,itwastheintuitionandvisionoftelecommu- nicationsresearchthatsiredthemicrocomputer. Inturn,thedevelopmentofcomputerand informationnetworksintheprivate,commercial,andmilitarysectorshaveplacedintensede- mandsontheessentialtechnologiesofhighdata-ratecommunication. Onasmallerscale,the trendtowardssmallerfeaturesizes,higherclockspeedsandincreasinglevelsofintegrationin microprocessorsisdrivingchiplevelcommunicationstothepracticalandtheoreticallimitsof metallization-interconnectmicrotechnology. Theanswertobothofthesetechnicaldilemmas maybethephoton. Drivenbytheeconomicsofbandwidth,fiber-opticssystemshaverevolu- tionizedlongdistancecommunications.Astheinformationdemandcontinuestogrowonan increasingly-localscale,itseemslikelythatopticalcommunicationssystemsmaybecome in- creasingly conspicuousfixturesinbusinesses,schoolsandhomes. Likewise,opticalintercon- nectshavethepotentialtomeetthespeedanddensityrequirementsofGHz-levelclockspeeds andmonolithicintegrationofcompletecomputingsystems.3 Opticalcommunicationssystemshavebeendesignedtooperateintheoptimalwavelength regimesforminimumsignalattenuationanddispersion. Thenearinfraredlossspectrumfor silicafibersisshowninFigure1-1.1 Radiativeintra-4fshelltransitionsinET+at1.54pm, allowedbycrystalfieldsplittingofdegeneratelevelsmatchtheattenuationlossminimain 1 2 FIGURE1-1 SilicafibersignalattenuationinthenearIR1 silicafibers. TheseenergylevelsaredepictedinFigure1-2.2 Asimilarcore-electrontransi- tioninthePr34ionproducesradiativeemissionat1.3pm,thesilicadispersionminima,which isanothersignificantopticalcarrierforfibercommunicationssystems.Theenergiesofthese intra-4fshelltransitionsintherare-earthionsarequitestableduetotheshieldingofthe4fshell levelsbythefilledouter5sand5porbitals.Table2liststheelectronconfigurationsofthe5s,5p, and4forbitalsfortherare-earthions.5Astheatomicnumberincreases,theoccupationofthe valence5s2p6shellremainsthesamewhileeachsuccessiveelectronintherare-earthseriesfillsthe 4forbitals.Thisorbitalfillingsequenceresultsinverysimilarchemicalpropertiesforallofthe rare-earthsbutarichopticalstructurethatisuniquetoeachion.Importantforoptoelectronics, theseintra-4fshelltransitionenergiesareeffectivelyshieldedfrommatrixeffectsbythe5sand5p 3 Er3+ EnergyLevels 4S3/2 0.54pm 2.0 4F,9/2 0.66pm > 4I,9/2 0.80pm ^ <u 4I11/2 0.98nm bn 1.0 wiaa-ji 4I13/2 ===iB 1.53pm m 0.0 - 4I15/2 free in ion matrix FIGURE1-2.Configurationofintra-4fshellenergylevelsinthefreeEr3*ionandafter crystalfieldsplittingoftheEr3+levelsinamatrix.2 4 electrons.Therefore,theemissionwavelengthoftheserare-earthtransitionsarelargelyindepen- dentofthehostmaterial. Highgain band-edgeandmultiplequantum-welllasersanddetectorsbasedontheIn- GaAsP/InP materialssystemwerealsodevelopedinordertotakeadvantageoftheoptimum infraredcommunicationwavelengthregimes.6However,systemsbasedonnarrow-gapInGaAsP activematerialssufferfrompoorwavelengthstabilityduetooperation-inducedtemperature driftoftheemissionline.Also,integrationofInGaAsPdeviceswithSimicroelectronicsforon- chipinterconnectsisacomplextask. Thelargelattice-mismatchofInGaAsPwithSiandthe sensitivityofthesematerialstodefectsprecludesanydirect,monolithicintegrationbyepitaxial growth.7Otherintegrationstrategiesbasedonphysicallybondingprefabricated,discreteoptical componentstoaSisubstratewouldbecomplex,expensiveanddifficulttoimplementinappli- cationssuchasmicroprocessorsordigitalsignalprocessingcomponentsthatwouldrequireahigh densityofinterconnects. Opticalfibersystemsachievinggainthroughstimulatedemissionfromopticallypumped rare-earthionsweredevelopedtoamplifysignalsintheopticaldomain.8Thesesystems,known asrare-earthdopedfiberamplifiers,donotsufferfromthetemperaturestabilityproblemsof semiconductorsystemsbasedonband-edgeemission. Theeffectivenessofthistechnology hasledtoEr-dopedfiberamplifiersbecomingwellestablishedinthelongdistance telecommunicationsindustry. However,drivingforcesforsimpler,moreefficient,lessexpensive andelectronically-integrated1.54pmgenerationandamplificationhavestimulatedinterestin developingalternativetechnologies.Theopticalpumpingsystemsrequiredinrare-earth-doped fiberamplifiersystemscanbeexpensiveandlarge. Also,typicalfibersystemshaveanoptical