Evolution of Ge and SiGe Quantum Dots under Excimer Laser Annea

.25,No.1(2008)242∗EvolutionofGeandSiGeQuantumDotsunderExcimerLaserAnnealingHANGen-Quan(韩根全)1∗∗,ZENGYu-Gang(曾玉刚)1,YUJin-Zhong(余金中)1,CHENGBu-Wen(成步文)1,YANGHai-Tao(杨海涛)2StateKeyLaboratoryonIntegratedOptoelectronics,InstituteofSemiconductors,ChineseAcademyofSciences,Beijing1000832Tsinghua-FoxconnNanotechnologyResearchCenter,DepartmentofPhysics,TsinghuaUniversity,Beijing1000841(Received15September2007)Wepresentdifferentrelax-tigationofthecoarseningandrelaxationofthedotsshowsthatthestraininGedotsonGefilmsisrelaxedbydislocationsincethereisnointerfacebetweentheGedotsandtheGelayer,whiletheSiGedotsonSi0.77Ge0.23filmrelaxbylatticedistortiontocoherentdots,whichresultsfromtheobviousinterfacebetweentheSiGedotsandtheSi0.77Ge0.23fiultsaresuggestedandsustainedbyVanderbiltandWickham’stheory,andalsodemonstratethatnobulkdiff:,,,dSiGeself-assembledquantumdots(SAQDs)arewidelystudiedfortheirpromis-ingapplicationinoptoelectronicsduetothree-dimensional(3D)quantumconfinement.[1]Manyworkshavefocusedonthegrowthmechanism,[2,3]shapetransition,[4,5]andthecoarseningprocessunderthermalannealing[6]-cently,weobtainedSiGequantumdotswithsmallsizeandhighdensitybyexcimerlaserannealing(ELA).[7]Thenanosecondpulsedurationoftheexcimer,whichinducesrapidheatingandcoolingofthesamplesur-face,ensuringthatthelaserinducedquantumdots(LIQDs)areformedonlybysurfaceatomsdiffusion.[8]WeobtainedGeandSiGelaserinducedquantumdotsbyELAoftheGeandSiGefilms,Letter,wereportthatthelaser-inducedGeandSiGequantumdotsundergodiff-force-microscopy(AFM)measurementsindicatethattheGeLIQDsontheGefilmrelaxbyformationofdislocation,whiletheSiGeLIQDsontheSi0.77Ge0.23filmreleasethorydevelopedbyVanderbiltandWickhamhasshown[9]thattheinterfacebetweenthedotsandthewettiSiGeLIQDsontheSi0.77Ge0.23film,ourcalculationshowsthatSiGequantumdotswiththeGecompositionofabout83%areformedontheSi0.77Ge0.23film,whichindicatesanobviousinterfacebetweenthedotsandtheSi0.77Ge0.23fir,fortheGeLIQDsontheGefilm,nointerfacebetweenthresuggestedandsus-∗Supported∗∗tainedbyVanderbiltandWickham’stheory,andalsodemonstratesthatnobulkdiffndSiGefilmsweregrownbyanultra-high-vacuumchemicalvapourdeposition(UHV-CVD)systemon(001)-orientedSisubstratesat500◦Cand550◦C,filmisinthicknessofabout1nm(8monolayers),andtheSiGefircesofSiandGearedisilaneandger-mane,ubstrateswerecleanedinanex-situchemicaletchprocessandloadedintoanUHVgrowthchamberwithbasicpressurelowerthan10−7Pa,andthenheatedupto950◦cknessandGecompositionoftheSi0.77Ge0.23filmaredeterminedbydouble-crystalx-raydiffraction(XRD).A193nmArFexcimerlaseroperatingfrequencyin40Hz,wasusedtoex-situannealthesamples,-flatbeamprofileof10×10mm2withtheenergydensityofabout180mJ/scarriedouttoensureuniforman-nealingofsamples’facemorphologyofthesampleswasmeasuredbyanSPA-300HVAFM,1showstheAFMimagesofGeandSiGeLIQDsobtainedbyELAofGeandSi0.77Ge0.23films,ghtprofimetersoftheGeandSiGeLIQDsare20–25nmand15–20nm,r-malprocessinducedbytheexcimerlaserpulseisonlyseveraltensnanoseconds,soduringtheELA,onlysurfacediffenergycanbeex-pressedbyE=4ΓV2/3tan1/3θ−6AVtanθ,[2]whereΓ=γdcscθ−γscotθistheincreaseofsurfaceenergy,b:hgquan@2008ChinesePhysicalSocietyandIOPPublishingLtd