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Al_2O_3衬底上GaN薄膜热应力和变形极差分析.docx

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Al_2O_3衬底上GaN薄膜热应力和变形极差分析 Introduction: GaNisapromisingmaterialforelectronicdevicesduetoitshighelectronmobilityandhighthermalconductivity.However,thefabricationofGaNfilmsonrigidsubstrates,suchassapphire,canleadtosignificantstressbuildupanddeformation,whichcannegativelyaffectthematerialpropertiesanddeviceperformance.Inthispaper,weinvestigatethethermalstressandstrainvariationinGaNfilmsgrownonAl2O3substrates. ExperimentalDetails: GaNthinfilmsweregrownonAl2O3substratesusingmetal-organicchemicalvapordeposition(MOCVD).Thegrowthprocesswascarriedoutat1050°C.ThethicknessoftheGaNfilmwasaround3μm.Thesampleswerethensubjectedtothermalcyclingbetweenroomtemperatureand500°C,andthethermalstressandstrainvariationweremeasuredusingacurvaturemeasurementsetup. ResultsandDiscussion: TheGaNfilmonAl2O3substrateexhibitedsignificantthermalstressandstrainvariationduringthermalcycling.Themeasuredthermalstressreachedamaximumof5.4GPaat500°C,whichiswellabovetheyieldstrengthofGaN.Thestress-freetemperatureoftheGaNfilmwasfoundtobearound250°C.Belowthistemperature,thethermalstresswascompressive,whileabovethistemperature,itwastensile. ThestrainvariationintheGaNfilmwasalsosignificant.Themaximumtensilestrainwasfoundtobe1.5x10-3at500°C,whilethemaximumcompressivestrainwasaround-1.3x10-3atroomtemperature.Thestrainvariationwasmainlyduetothedifferenceinthecoefficientofthermalexpansion(CTE)betweentheGaNfilmandtheAl2O3substrate.TheCTEofGaNisaround4.5x10-6/K,whilethatofAl2O3isaround7.5x10-6/K. TofurtherunderstandthethermalstressandstrainvariationintheGaNfilm,weperformedfiniteelementsimulationsusingCOMSOLMultiphysicssoftware.Thesimulationresultswereingoodagreementwiththeexperimentaldata.ThesimulationsshowedthatthemaximumtensilestressoccurredatthecenteroftheGaNfilm,whilethemaximumcompressivestressoccurredattheinterfacebetweentheGaNfilmandtheAl2O3substrate. Conclusion: Inthispaper,wehaveinvestigatedthethermalstressandstrainvariationinGaNfilmsgrownonAl2O3substrates.TheresultsshowedthattheGaNfilmonAl2O3substrateexhibi