材料物理.docx
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材料物理.docx
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材料物理
GaN-basedsemiconductormaterial
113116001151GaoXin
Abstract
Semiconductorhasmanyuniquephysicalproperties,whicharecloselyrelatedwiththeelectronicstatesinsemiconductorsandmovementcharacteristics.Thesemiconductorwhichabsorbssomeenergyelectronscanbeexcitedphotons.Similarly,electronsintheexcitedstatecantransitiontoalowerenergylevelandreleaseenergyintheformofopticalradiation.Thatistosay,electronsfromhighenergyleveltoalowerenergyleveltransitions,accompaniedbyelectronemission.Thisisthesemiconductorlight-emittingphenomenon.Dependingondeferentexcitationmethods,therearevariousemissionprocess,suchaselectroluminescence,photoluminescenceandcathodoluminescence.
AsthethirdgenerationofsemiconductormaterialswhichreferstoGaN,InNandAlN,GaNrealizestheemissionofshortwavelaisersuchaspurplelight,bluelight,greenlightandultravioletlight.GaNlaiserplaysanimportantroleinthestorageofhighdensityopticalinformation,deep-seacomunication,laiserdisplayandlaiserprinting.Inthispaper,thestructure,characteristicsandapplicationofGaNlasersmadeabriefpresentation.
1.Introduction
Innatureandeverydaylife,luminousphenomenoneverywhere.Withthedevelopmentofproductionandscienceandtechnology,peopleareincreasinglywidespreaduseofavarietyoflightemittedbythelightsource,tomeetthevariousneedsofdifferentapplications.Forexample,thelightforillumination,measurement,studythestructureofmatterandforavarietyofmilitarytechnologybeing[1].Withthedevelopmentofopticalapplications,peopleareincreasinglyhighrequirementsoflightandhopethereislightemissionintensityashighaspossible,hopingemittedlightinonlyonedirectionparallelout,hopingthelightsourcecanemitasinglecolor.Finally,in1960,itsuccessfullydevelopedamethodtomeetthesethreerequirements,withordinarylightemittingmechanismcompletelydifferentnewlight-laser.[2]
GaNmaterialsareGaN,InN,AlNandmulti-alloymaterialcomposedofthem.Byadjustingthealloycompositioncanbeobtainedcontinuouslyadjustable1.9-6.2eVbandgapenergy,sotheGaN-basedmaterialtocoverthespectrumfromultraviolettoredlight,thusbecomingashortwavelengthoptoelectronicdevicesandhigh-frequency,high-pressure,high-temperaturemicroelectronicdevicePreparationofmaterialismostpreferred[3].
1.1Semiconductorelectronicstate
Materialsusedformanufacturingsemiconductordevicesaremostlysinglecrystal.singlecrystalisformedbyperiodicarrangementofatomsandadjacentatomicdistanceonlyafewtenthsofnanometers.Thereforecertainlysemiconductorandelectronicstateofthedifferentatoms,especiallytheouterelectronvarysignificantly,however,thecrystalisformedbyaggregationofdiscreteatoms,andtheelectronicstateofthetwomusthavesomelink.Electronicsandsemiconductorcrystalsisolatedatomicelectrondifferent,andfreedomofmovementofelectronsisdifferent.Isolatedatomicelectronisstrictlybetweentheperiodicarrangementofatomsinmotion.Single-electronapproximationbelievethatcrystalsoneelectronisinthecyclicalchanges,andit'sthesamecycleandthelatticeperiod.studyfoundthatthebasiccharacteristicsofelectronsinaperiodicpotentialfieldisverysimilarwiththefreemovementofelectronmotion.
Freeelectronwavefunction
.Crystalwavefunction(Blochfunction)
wherekisthewavenumberandukisaperiodicfunctionwiththeperiodofthelattice.Inotherwords,
wherenisaninteger.Fromcomparisonoftwowavefunctions,intheformofthewavefunctionandthefreeelectronwavefunctionofelectronsinacrystalperiodicpotentialfieldsportsimilar,whichrepresentsaplanewavepropagatinginthekdirectionwiththewavelength
.Buttheamplitudeofthewavewithxperiodicallychanges,thesameperiodicityandthelatticeperiod.Sothatthecrystalisanamplitudeoftheelectronicwavepropagationinthecrystalplaneelectroniclongertotallyconfinedwithanatom,butmaymovefreelyfromonepointtothecorrespondingpointinanothercellwithintheunitcell.thuselectronsthroughoutthecrystalmovement,thismovementiscalledatotalofmotionofelectrons.consistingofatotalofouterelectronsofcrystalatomsstrongmovement,oftencalledquasi-freeelectrons,whilethetotalofthemovementofelectronsthantheinnerweak,theirbehaviorwithisolatedatomicelectronsimilarfunctionintheBlochwavevectorkandfreeelectronssimilartokdifferenttotalmarksofdifferentstateofmotion.[1]
1.2StructureofGaNcrystalstructure
GaNhastwosphaleriteandwurtzitestructure.Sphaleritestructuresimilartodiamondlatticestructure,whichconsistsofthetwotypesofatomsintheirface-centeredcubiclattice,thedisplacementalongthespacediagonalofeachquarterconfigurationfromasetofdiagonallengthandeachatomissurroundedbyfouralienatoms,forexample,iftheangleofthetopsurfaceoftheheartandⅲatomsareatoms,theatomsintheunitcell4istheinternalⅴatoms,whereasversa.betweenatomscovalentlybondedtorely,buttherearecertainioniccomponent.Semiconductorsphaleritestructure,covalentbondtosp3hybridorbitalbasis.Becauseofthiscovalentcompoundsemiconductors,combiningnaturewithvaryingdegreesofionic,sooftencalledsemiconductorssuchaspolarsemiconductors.wurtziteandsphaleritearesimilar,butalsotoformthebasisofaregulartetrahedronstructure,butithasahexagonalsymmetry,ratherthancubicsymmetry.Itbilayerhexagonalarrangementoftheiratomsinthetwogroupsconsistingofpiledup,itisonlytwotypesofhexagonalatomiclayersstackedintheorderABABABAB......byits(001)planetotherules,therebyformingafirststructureofzinc.Inwurtzitecrystalcovalentcompound,whichiscombinedwithanionicnature,butthetwoelementselectricallylargenegativedifference,ifthedominantionicbond,thenittendstoformawurtzite.[1]
1.3Theprincipleoflasergenerated
Similarly,electronsintheexcitedstatecantransitiontoalowerenergylevelandreleaseenergyintheformofopticalradiation.Thatistosay,electronsfromhighenergyleveltoalowerenergyleveltransitions,accompaniedbyelectronemission.Thisisthesemiconductorlight-emittingphenomenon.Dependingondeferentexcitationmethods,therearevariousemissionprocess,suchaselectroluminescence,photoluminescenceandcathodoluminescence.[2]
Thecompositionofthematerialundernormalcircumstancesthemajorityofelectronsinthegroundstate,theelectronabsorptionwhentheexternalenergy,thetransitionfromthelowstatetoahigherenergystate,whereaswhentheelectrontransitionsfromahigherenergystatetothegroundstate,thelightemittedorenergyandsoon.Ifthetransitionenergyreleaseiscalledradiativetransition;Ifyoudonotemitlightandotherformsofenergyrelease,callednon-radiativetransition.Statetransitionofelectronsfromhigh-energyphotonsemittedbacktoalowerenergystateiscalledspontaneousemission.Undernormalcircumstances,ordinarylight-emittingprocessarespontaneousemission.Duetothenumberofelectronscanbegatheredinthehighlyexcitedstatesislimited,andtheseelectronsmaybeinadifferentenergylevel,sorelativelyfewnumberofphotonsemittedphotonsemittedfrequencyisnotuniform,itisdifficulttoachievehighstrength,singlefrequency,requiresasingledirection.
Mentionedabove,undernormalcircumstances,mostofthemaregatheredintheelectronicgroundstate,onlyafewelectronsinhighlyexcitedstates.InhighlyexcitedstatesofelectronsthroughspontaneoustransitiontothegroundstateandemitsaphotonwhoseenergyisEPhoton=EHigh-energystate-ELow-energystate=hν,conversely,ifthesameenergyoftheincidentphotonsfromtheoutsideofthesubstance,theelectronsinthegroundstateandthetransitiontoabsorbtheincidentphotonexcitedhighenergystate.Thisprocessiscalledtheresonantabsorptionofincidentlightonthematerialtransitions.Weusesomeartificialmeans,sothatmostoftheelectronicgroundstatebutnotgatheredinhighlyexcitedstatesofaggregationinthiscasethepresenceofthehighlyexcitedelectronicstates,alargenumberofsmallelectronicgroundstate,thisstateiscalledpopulationinversion.Inthisstate,theemergenceofanewtransmission.Inthecaseofpopulationinversion,whenthephotonwiththeenergyofEPhoton=hνincident,electronsintheexcitedstate,thetransitionoftheincidentphotonsintheexcitationtothegroundstate,whilealargenumberofphotonsemitted,theprocesstransitionsstimulatedphotonsemittedbytheincidentphotonidenticalcharacteristics.Suchisthestateoftheaboveactsinversionworkingsubstancecalledstimulatedemissionoflight.Thenumberofstimulatedemissionofphotons,thenumberofparticlesandreverseproportionaltothenumberofincidentphotons.Alaseroscillatoriscontrolledbythestimulatedemissionoflight.
2.GaN-basedlaser
2.1Semiconductorlasers
Thelasercanbedividedintoasolidlaser,agaslaser,asemiconductorlaser.Theuseofopticallypumpedsolid-statelaserstoachievepopulationinversion,willworktogrowcylindricalmaterialprocessing,theupperandlowersectionsoftwoparallelplanemirrorpolishedreflectivesurfacecomposedofresonantcavity.Gaslasersusingelectricalinjectionmeanstoachievepopulationinversion,andthenumberofparticlesbyresonanceenergytransfertoachie
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