Optical properties of CdTe below and above the band edge

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1、OpticalpropertiesofCdTebelowandabovethebandgapP.HorodyskýandP.HlídekInstituteofPhysics,CharlesUniversity,PragueDirectmeasurementofinterbandabsorptiononverythinsamplesContentPreparationofthinsamplesAbsorptioncoefficientclosetotheenergybandgapQualityofultra-thinsamplesTemperaturede

2、pendenceoffreeexciton(FX)peakinabsorptionPreparationofthinsamplesStartingmaterial-highqualityCdTemonocrystalsMechanicalpolishingsamplesgluedonquartzorsaphiresubstrate(thickness1-5m)freestandingsamples(thickness10-20m)Chemicaletching(bybrom-methanol),removalofseveralmgluedsampl

3、es(onlyoneside)freestandingsamples(bothsides)Minimalthicknessgluedsamples0.8mfreestandingsamples4.8m(3x3mm2)CdTeSubstrateMicronthicksamplegluedonsubstrateAbsorptionspectraofthinandthicksamplesroomtemperatureAbsorptiontailonboth-sideetchedsampleismuchweakerEnergybandgapofCdTeat

4、RTis1.50-1.51eVAbsorptionedgeon‘thick’sampleisfarfromEgOccupationofedgestatesduringphotoluminescenceexcitationroomtemperatureRTPhotoluminescencearisesfrombothlocalisedandfreestatesbellowandaboveEgPhotoluminescencefromthinfree-standingsamplelowtemperaturePhotoluminescencefrom3m

5、belowthelong-timepolishedsurfaceehibitsonlyslightlymorebroadenedboundexcitonlinescomparedtostandardhigh-qualityPLspectrumAbsorptionofthinfree-standingsamplelowtemperatureModelforfittingthetransmittancespectrummodulatedbyinterferencebellowEg:lossesbyreflectanceR(E)+absorption(two

6、exponentialfunctionsforabsorptiontail)refractiveindexn(E)takenfromHlídeketal.,RefractiveindexofCdTe:Spectralandtemperaturedependence,J.Appl.Phys.90(4),2001AbsorptionandPhotoluminescencefromultra-thinsamplelowtemperatureMoredetails:Grilletal.,Defect-inducedopticaltransitionsinCdT

7、eandCd0.96Zn0.04Te,Semi.Sci.Tech.17,2002MoredetailsonFX+LOabsorption:Dillingeretal.,Phonon-AssistedExcitonTransitionsinAIIBVIsemiconductors,Phys.Stat.Sol.29,1968AbsorptionandPhotoluminescencefromultra-thinsamplelowtemperatureFXlinewidthoffree-standingsampleis3-4timesnarroverAbov

8、eEgabsorptiononafree-standingsamplenotac