GaAsGaAlAs超晶格的光电流谱研究(英文)-豆柴文库

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GaAsGaAlAs超晶格的光电流谱研究(英文)
StudyofPhotocurrentSpectraofGaAs/GaAlAsSuperlattice
Superlatticeshavebeenasubjectofintenseresearchinthefieldofsemiconductorphysicsduetotheiruniquepropertiesandpotentialapplications.GaAs/GaAlAssuperlatticesareaparticularlyinterestingsystembecauseoftheirhighcarriermobilityandtunablebandgap,whichallowsforfinecontroloftheelectronicandopticalproperties.Inthisstudy,weinvestigatethephotocurrentspectraofaGaAs/GaAlAssuperlatticesampleusingphotoluminescenceexcitationspectroscopy(PLE).
Thesamplewasgrownbymolecularbeamepitaxy(MBE)onasemi-insulatingGaAssubstrate.ThesuperlatticeconsistsofalternatinglayersofGaAsandGaAlAswithaperiodof100Å.ThethicknessoftheGaAsandGaAlAslayerswas50Åeach.Thesamplewasthencleavedintoa2mmx2mmsquareandmountedonacoldfingerinaliquid-heliumcryostatfortemperature-dependentmeasurements.
Tomeasurethephotocurrentspectra,weusedahome-builtPLEsetupwithaHeCdlaserastheexcitationsource.Thelaseroperatesatawavelengthof325nm,whichisabovethebandgapofGaAsandGaAlAs.Thelaserlightisfocusedontothesampleusingamicroscopeobjectivelenswithaspotsizeof10μm.Thesignalfromthephotocurrentwasmeasuredusingalock-inamplifierwithachoppingfrequencyof634Hz.
Wefirstmeasuredthephotoluminescence(PL)spectraofthesampletoconfirmthequalityofthesuperlattice.ThePLspectrumshowedseveralsharppeaks,whichcorrespondedtothetransitionsbetweentheconfinedgroundstatesoftheGaAsandGaAlAsquantumwells.Theenergyseparationbetweenthepeaksisconsistentwiththedesignedbandgapofthesuperlattice.
Next,wemeasuredthePLEspectrabyscanningtheexcitationlaserwavelengthfrom680nmto890nmwhilemonitoringthephotocurrentsignal.ThePLEspectrashowedaseriesofpeaksthatcorrespondedtothetransitionsbetweentheconfinedstates.Thepeakenergiesshiftedwithchangingexcitationwavelength,indicatingthatthebandgapofthesuperlatticeistunablethroughexternalexcitation.
TofurtheranalyzethePLEspectra,wefitthedatatoamodelbasedontheeffectivemassapproximation.Themodelincludestheone-dimensionalconfinedstatesintheGaAsandGaAlAslayersandaccountsfort