Effects of laser irradiation on the structure and optical pr

MaterialsLetters64(2010)2072–2075

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MaterialsLetters

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EffectsoflaserirradiationonthestructureandopticalpropertiesofZnOthin lms

HuiLua, ,YaoquanTub,XianLina,BinFangc,DuanbinLuoa,AattoLaaksonend

a

DepartmentofPhysics,EastChinaUniversityofScienceandTechnology,Shanghai200237,ChinaSchoolofScienceandTechnology,ÖrebroUniversity,70182Örebro,Swedenc

InstituteofNuclearPhysics,EastChinaUniversityofScienceandTechnology,Shanghai200237,Chinad

DivisionofPhysicalChemistry,DepartmentofMaterialsandEnvironmentalChemistry,StockholmUniversity,S-10691Stockholm,Sweden

b

articleinfoabstract

TheeffectsoflaserirradiationonthesurfacemicrostructureandopticalpropertiesofZnO lmsdepositedonglasssubstrateswereinvestigatedexperimentallyandcomparedwiththoseofthermalannealing.X-raydiffraction(XRD)andatomicforcemicroscopy(AFM)measurementsshowedthattheirradiationtreatmentwithanAr+laserof514nmfor5minimprovesthecrystallinequalityofZnOthin lmsthroughincreasingthegrainsizeandenhancingthec-axisorientation,withtheeffectssimilartothoseofthethermalannealingat500°http://doc.guandang.netserirradiationwasfoundtobemoreeffectivebothfortherelaxationoftheresidualcompressivestressintheas-grown lmsandforthemodi cationofthesurfacemorphology.Asigni cantincreaseintheUVabsorptionandawideningintheopticalband-gapofthe lmswerealsoobservedafterlaserirradiation.

©2010ElsevierB.V.Allrightsreserved.

Articlehistory:

Received13March2010Accepted10June2010

Availableonline22June2010Keywords:Thin lms

SemiconductorsLasertreatmentAnnealing

MicrostructureOpticalproperties

1.Introduction

Zincoxide(ZnO)belongstoII-VIcompoundsemiconductorsand,atroomtemperature,hasadirectbandgapof3.37eV.Therefore,ithasbeenrecognizedasapromisingphotonicmaterialintheUVregion[1,2].ZnOmaterialsalsopossessmanyuniquepropertiesforotherapplications,suchassolarcells,surfaceacousticwavedevices,varistors,gassensors[3–6],andsoon.InordertoproducehighqualityZnOthin lms,appropriatedepositiontechniquesandoptimaldepositionconditionsareessential.However,post-treat-mentsofas-deposited lmsarealsonecessary,astheyplayasigni cantroleinimprovingthecrystallinequalityandmodulatingthe lmproperties[7].Conventionalfurnaceannealing(CFA)andrapidthermalannealing(RTA)arewidelyknownastheeffectivetechniquestoimprovethecrystallinequality[8,9].Inrecentyears,laserirradiationhasemergedasapowerfulmethodformodifyingthepropertiesofmaterialsurfaces[10,11].Comparedwiththeclassicannealingmethod,laserirradiationpossessessomedistinc-tiveadvantages,suchasrapidlocal-heating,reducedthermalexposureofthesample,lowin uenceonthesubstratetemperature,and exiblemanagement.

Inthiswork,anAr+laser(514nm)hasbeenemployedtoirradiatetheZnOthin lmsdepositedundercertainconditions.Theirradiationeffectsofthelaseronthestructureandopticalpropertiesofthe lms

wereinvestigatedandcomparedwiththoseofthethermalannealingat500°C.Basedontheexperimentalresults,wepresentapost-treatmentmethodofeffectivelymodifyingthesurfacepropertiesofZnOthin lms.

2.Experimentaldetails

TheZnOthin lmsampleswerepreparedbythegasdischargeactivatedreactionevaporation(GDARE)depositionmethod[12].Thedepositionconditionswerethatthesubstratetemperature,dischargevoltage,evaporationcurrent,oxygenpressure,anddepositiontimewere150°,-800v,25A,13Pa,and20min,respectively.Thesamplesdepositedwerefurtherpidedintothreepiecesandtwoofwhichwerepost-treatedintheair.Sample-awastheas-grown lmandsample-bwasannealedat500°Cfor1h,whilesample-chadbeenirradiatedatroomtemperaturefor5minusinganAr+laserwiththewavelengthof514nmandpowerof290mW.Thelaserbeamhasadiameterof3mm.

Thesurfacemorphologyandcrystalstructuresofthesampleswerecharacterizedusingatomicforcemicroscope(AFM,AJ-III)andX-raydiffraction(XRD,RigakuDMAX/VB),respectively.TheiropticalabsorptionspectraweremeasuredbyaUV-VIS-NIRspectrophotom-eter(CARY-500)inthewave-lengthrangeof300nmto1000nm.3.Resultsanddiscussion

ThevariationofthesurfacemorphologyoftheZnOthin lmswasstudiedbyAFMimagesandisshowninFig.1.Theas-grown lm(sample-a)hasarelativesmoothanddensesurfacemorphologyand

Correspondingauthor.Tel.:+862164253101;fax:+862164530721.E-mailaddress:luhui@http://doc.guandang.net(H.

Lu).0167-577X/$–seefrontmatter©2010ElsevierB.V.Allrightsreserved.doi:

10.1016/j.matlet.2010.06.022

H.Luetal./MaterialsLetters64(2010)2072–20752073

Fig.1.AFMimageoftheZnOthin lms:(a)sample-a,(b)sample-b,and(c)

sample-c.

exhibits neuniformly-distributedmassif-likeZnOgrainswithsizesintherangeof50-150nm(Fig.1(a)).ComparingFig.1(b)and(c),thereisamarkeddifferencebetweenthesurfacemicrostructuresof

theZnOthin lmstreatedbythethermalannealing(sample-b)andlaserirradiating(sample-c).Sample-bshowsanevenagglomerationofsmallmassif-likeZnOgrainswithsizesintherangeof80-300nm.Forsample-c,wecanseethattheaggregatesofZnOgrainsarepolygon-shapedwithrelativelyregulargrainboundaryand,be-tweentheaggregates,thereexistdeepslitsandbigpunctures.Thisisaninterestingphenomenon,whichimpliesthedevelopmentoflateralfacetsoftheZnOgrainsafterlaserirradiating.ThesizeoftheZnOgrainaggregatesisalsobiggerthanthatofsample-bandismainlydistributedintherangeof200nm,250nm,400nm,and500nm.

Fig.2(a),(b),and(c)aretheXRDpatternsofsample-a,sample-b,andsample-c,respectively.Table1showsthelatticeconstant,position,andtheFWHMof(002)peaksofthesamples.Obviously,allthe lmsexhibitmainlytheprominent(002)diffractionpeak,indicatingthatthepreferentialorientationisalongthec-axisperpendiculartothesubstratesurface.TheXRDspectrarevealthein uenceofthelaserirradiationandthermalannealingonthestructureoftheZnOthin lms.WecanseefromFig.2andTable1thatthe(002)diffractionpeaksofsample-bandsample-cbecomestrongandnarrow,indicatingthatgraingrowthhasoccurred,andshifttohigher2θanglesduetothevariationandpartialreliefofresidualstres …… 此处隐藏：10621字，全部文档内容请下载后查看。喜欢就下载吧 ……