光电子学-南京邮电大学中国大学mooc课后章节答案期末考试题库2023年

光电子学_南京邮电大学中国大学mooc课后章节答案期末考试题库2023年Photogenerationoccursintheneutralregion.Theelectronhastodiffusetothedepletionlayerandthenrolldowntheenergyhilli.e.driftacrosstheSCL.

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PhotogenerationinsidetheLEDgeneratesanelectronandahole.

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ThefifthvalenceelectroncanbereadilyfreedbythermalvibrationsoftheSilattice.

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TheareaunderpE(E)versusEisnottheholeconcentration.

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vdh=Driftvelocityoftheholes

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Wavelengthsgreaterthanroughlylgarenotabsorbed(byband-tobandtransitions).

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Whenitmovesadistancedx,workmustbedonebytheexternalcircuit.Intimedt,theelectrondriftsadistancedxanddoesanamountofworkeEdx

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TheelectronisnotactedonbytheforceeEoftheelectricfield.

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ThecavityinVerticalCavitySurfaceEmittingLasersisnotvertical.

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Externalphotocurrentduetothemotionofthisphotogeneratedelectronisie(t).

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IfEFisclosetotheconductionband(CB)edge,Ec,itresultsinann-type,andifitisclosetothevalenceband(VB)edge,Ev,itresultsinap-typesemiconductor.

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Anelectronandholepair(EHP)isphotogeneratedatx=y.Theelectronandtheholedriftinoppositedirectionswithdriftvelocitiesvhandve

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AnopencircuitpnjunctionunderilluminationgeneratesanopencircuitvoltageVoc.

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Thepnjunctioninopencircuit.Thephotogeneratedelectronandholerolldowntheirenergyhills(drift)butthereisavoltageVocacrossthediodethatcausesthemdiffusebacksothatthenetcurrentiszero.

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Lightfromanopticalfiberiscoupledintotheactiveregionofthelaserstructure.Astheradiationpropagatesthroughtheactivelayer,opticallyguidedbythislayer,itbecomesamplifiedbytheinducedstimulatedemissions,andleavestheopticalcavitywithahigherintensity.

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Travelingwave(TW)semiconductoropticalamplifier:Theendsoftheopticalcavityhaveantireflection(AR)coatingssothattheopticalcavitydoesnotactasanefficientopticalresonator,aconditionforlaser-oscillations.

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ThecrosssectionofVerticalCavitySurfaceEmittingLasersiscircular.

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Themodefielddiameterisnormallylargerthantheactivelayerthicknessandtheradiationspreadsintotheguidinglayer.

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PartiallyreflectedwavesatthecorrugationscanonlyconstituteareflectedwavewhenthewavelengthsatisfiestheBraggcondition.

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RateofelectroninjectionbycurrentI=Rateofspontaneousemissions-Rateofstimulatedemissions

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Whenthelaserisinasteadystate,Rateofcoherentphotonlossinthecavity=Rateofstimulatedemissions

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PowerConversionEfficiency=Opticaloutputpower/Electricinputpower

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Extractionefficiency=(Totalloss)/(Lossfromtheexitcavityend)

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ThewidthoftheCBiscalledtheelectronaffinityχ.

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TheinteractionsbetweentheSiatomsandtheirvalenceelectronsresultintheelectronenergyinthecrystalfallingintotwodistinctenergybandscalledthevalenceband(VB)andconductionsband(CB).

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Atsufficientlyhighdiodecurrentscorrespondingtohighopticalpower,theoperationbecomessinglemode.

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InLED,mostofthelightisintheactiveregion.

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Inmultiplequantumwell(MQW)heterostructurelaserdiode,electronsareinjectedbytheforwardcurrentintoquantumwells.

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Thedensityofsatesg(E)isastep-likefunction,andisfiniteatE1andE1¢.

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Aburiedheterostructurelaserdiodefortelecomapplications:Theactivelayer(InGaAsP)issurroundedbythewiderbandgap,lowerrefractiveindexInPmaterial.LayersaregrownonanInPsubstrate.

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Adoubleheterostructuresemiconductorlaserdevicehasitsactiveregionburiedwithinthedeviceinsuchawaythatitissurroundedbylowrefractiveindexmaterialsrenderingtheactiveregionasawaveguide.

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RobertHallandhiscolleagues,whileworkingatGeneralElectric'sResearchandDevelopmentCenterinNewYork,wereamongthefirstgroupsofresearcherstoreportaworkingsemiconductorlaserdiodein1962.

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Insemiconductorlaserdiode,banddiagramdoesnotneedasufficientlylargeforwardbiastocausepopulationinversionandhencestimulatedemission.

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Arandomphoton(fromspontaneousdecay)ofenergyhu21=E2-E1cannotinitiatestimulatedemission.

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AsthestatesatE2arelong-lived,theyquicklybecomepopulatedandthereisapopulationinversionbetweenE2andE1.

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IonsatE3rapidlydecaytothelong-livedstateattheenergylevelE2byemittinglatticevibrations(phonons).

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Manyphosphorsarebasedonactivatorsdopedintoahostmatrix.

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LightcouldnotbecoupledfromasurfaceemittingLEDintoamultimodefiberusinganindexmatchingepoxy.

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Impactofanenergeticconductionelectronwithcrystalvibrationstransferstheelectron'skineticenergytoavalenceelectronandtherebyexcitesittotheconductionband.

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AnRCLEDisanLEDwithanopticalresonantcavity(RC)formedbytwoDBRshasanarroweremissionspectrum.

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Recombinationaroundthejunctionandwithinthediffusionlengthoftheelectronsinthep-sideleadstospontaneousphotonemission.

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ThemostuselesspropertyofEFisintermsofachangeinEF.

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Eg=Ev-Ec

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Theelectronsataparticularenergylevelalsohavekineticenergiesintheyzplane,whichisnotquantized.

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Potentialenergyischarge*potential=qV

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Anelectroninthen-sideatEcmustovercomeapotentialenergy(PE)barriertogoovertoEcinthep-side.ThisPEbarrieriseVowhereVoisthebuilt-inpotential,i.e.,themaximumextentEchasbeenbenttolineuptheFermilevels.

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TheEHPrecombinationthatoccursintheSCLandtheneutralregionsinthisGaAspnjunctioncasewouldresultinphotonemission,withaphotonenergythatisapproximatelyEg.ThisdirectrecombinationofinjectedminoritycarriersandtheresultingemissionofphotonsrepresenttheprincipleofoperationoftheLightEmittingDiode(LED).

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TheincreasedVresultsinanincreasedIinthediodecurrent.Thedynamicorincrementalresistanceisrd=dV/dI.

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InaGepnjunction,above238K,Ireviscontrolledbyni2andbelow238Kitiscontrolledbyni.

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Ec=Fermienergy,EF=Conductionbandedge

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nadegeneratesemiconductor,onecannotassumethatn=Ndorp=Na,asthedopantconcentrationissolargethattheyinteractwitheachother.Notalldopantsareabletobecomeionized.Thesaturationistypicallyaround1020cm-3.

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Na<

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AtroomtemperaturethethermalvibrationsofthelatticecanfreetheholeawayfromtheB-site.

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ThereareacceptorenergylevelsjustaboveEvaroundB-sites.Theseacceptorlevelsacceptelectronsf