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NANOEXPRESSOpenAccessStructuralandopticalcharacterizationsofInPBithinfilmsgrownbymolecularbeamepitaxyYiGu1,KaiWang1,HaifeiZhou1,YaoyaoLi1,ChunfangCao1,LiyaoZhang1,YonggangZhang1,QianGong1*andShuminWang1,2*AbstractInPBithinfilmshavebeengrownonInPbygassourcemolecularbeamepitaxy.
AmaximumBicompositionof2.
4%isdeterminedbyRutherfordbackscatteringspectrometry.
X-raydiffractionmeasurementsshowgoodstructuralqualityforBicompositionupto1.
4%andapartiallyrelaxedstructureforhigherBicontents.
Thebandgapwasmeasuredbyopticalabsorption,andthebandgapreductioncausedbytheBiincorporationwasestimatedtobeabout56meV/Bi%.
StrongandbroadphotoluminescencesignalswereobservedatroomtemperatureforsampleswithxBi180Kthepeakataround0.
95eVdisappearsandtheothertwopeaksareoverlapped.
Thepeakenergieslabeledpeaks1and2redshiftedabout82and108meV,respectively,whenthetemperatureincreasesfrom8to300K,compar-abletothered-shiftedvalueof71meVfortheInPrefer-encesample.
However,thepeakenergieslabeledpeak3arealmostconstantataround0.
95eVatvarioustempera-tures.
Toourknowledge,thePLsignalofdilutebismidesfarfromtheband-to-bandtransitionwasscarcelyreportedFigure3BandgapenergyofInPBimeasuredfromabsorptionspectraasafunctionofBicomposition.
Theerrorbarsoftheexperimentaldataarelabeled.
Thesolidlineisthefittinglineoftheexperimentaldata.
Figure4PLspectraofInPBifilmswithvariousBicompositionsatRT.
ThePLspectrumofInPreferencesampleisalsoshown.
Guetal.
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Markoetal.
observedtheclearandbroadPLsignalofInGaAsBisamplefrom0.
46eV(2.
7μm)to0.
65eV(1.
8μm)withamuchlongerwavelengththantheband-to-bandPLat0.
786eV(1.
6μm)andattributedtothecompositionalinhomogeneity[19].
Theysuggestedthatthelocalizednarrower-gapregionstrappedcarriersatlowtemperaturesandproducedthelongwavelengthemis-sion.
However,theycouldonlyobservethelongwave-lengthPLatT<160K,andthePLintensitydroppedrapidlywithtemperature,whichcontraststoourresults.
Inaddition,transmissionelectronmicroscopeandsecond-aryionmassspectrometrymeasurements(notshownhere)haverevealedquiteuniformBicontentsinourInPBisamples.
AnotherpossibleexplanationisthatthelongwavelengthPLisfromtherecombinationrelatedtodeepenergylevels.
TheBiincorporationatlowgrowthtemper-aturesmayintroduceBi-relateddefectssuchasBi-antisites[20],whichcouldactasadeeprecombinationcenter.
Notethattheband-to-bandPLofInPBiwasnotobservedevenat8Kinourexperiments.
Thissuggestsaveryshortcarrierlifetimeatthebandgapandalongcar-rierlifetimeatthedeeplevels.
Therefore,theoriginofthePLsignalsisstillunclearatpresent,andfurtherinvestiga-tionsareneededtofullyaccountforthisphenomenon.
ConclusionsThestructuralandopticalpropertiesof430-nm-thickInPBithinfilmshavebeeninvestigated.
TheBicomposi-tionsdeterminedbyRBSmeasurementswereintherangeof0.
6%to2.
4%.
AgoodqualityhasbeendemonstratedforthesampleswiththeBicompositionlowerthan1.
4%,whereasthesampleswithhigherBicontentsbecomepar-tiallyrelaxed.
ItwasfoundthattheincorporationofBicausedthebandgapreductionofabout56meV/Bi%.
StrongandbroadPLsignalscontainingmultipleover-lappedpeakswereobservedatroomtemperaturewithpeakwavelengththatvariedfrom1.
4to1.
9μm,whichisfarfromtheband-to-bandtransition.
TheoriginsofthelongwavelengthPLsignalswerediscussed,butfurtherin-vestigationisnecessaryforunambiguousexplanation.
CompetinginterestsTheauthorsdeclarethattheyhavenocompetinginterests.
Authors'contributionsYGcarriedouttheopticalmeasurements,analyzedtheresults,andwrotethemanuscript.
KWgrewthesamplesandperformedXRDmeasurements.
HFZ,YYL,CFC,andLYZhelpedinthemeasurementsandanalysisofresults.
YGZsupervisedthePLexperimentsandrevisedthemanuscript.
QGsupervisedthegrowthandjoinedthediscussions.
SMWproposedtheinitialwork,supervisedthesampledesignandanalysis,andrevisedthemanuscript.
Allauthorsreadandapprovedthefinalmanuscript.
AcknowledgementsTheauthorswishtoacknowledgethesupportofNationalBasicResearchProgramofChinaundergrantnos.
2014CB643900and2012CB619202;theNationalNaturalScienceFoundationofChinaundergrantnos.
61334004,61204133,and61275113;theGuidingProjectofChineseAcademyofSciencesundergrantno.
XDA5-1;theKeyResearchProgramoftheChineseAcademyofSciencesundergrantno.
KGZD-EW-804;andtheInnovationResearchGroupProjectofNationalNaturalScienceFoundationundergrantno.
61321492.
Received:13November2013Accepted:18December2013Published:13January2014Figure5PLspectraoftheInPBisamplewith1.
0%Biatvarioustemperatures.
Theoverlappedmulti-peaksobtainedbyusingGaussianfittingareshownasthedashedanddottedlinesforthecasesof8and300K,andthemulti-peaksofPLspectraatothertemperatureswerealsoobtainedsimilarly.
Figure6PLenergiesofthemulti-peaksatvarioustemperaturesfortheInPBisamplewith1.
0%Bi.
Theenergyvalueswereextractedbyusingthemulti-peakGaussianfittingofthePLspectraatvarioustemperatures.
Guetal.
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