关于多孔硅(3)

多孔硅在太阳电池中应用有着很大的 潜力。

R.Bilyalovetal./SolarEnergyMaterials&SolarCells65(2001)477}485479

Fig.1.XTEMimageofSi"lmgrownonPS(%).Table1

DefectdensityasderivedfromplanviewTEM-analysisforthinSi"lmsepitaxiallygrownusingDCSat7253Consingleanddualporouslayers

Region

Epi-Si"lm('100nmfromtheinterface)

Epi-Si/PSinterface("rst100nm)20%porosity(10 cm\ n.a.60%porosity3.5;10 cm\ 3.5;10 cm\ dualporosity(10 cm\ 1;10 cm\

su$cienttoobtainanappropriatecrystallographicquality.Forthedualporouslayerstructure,thedefectdensityneartheSi/porousSiinterfaceishigher(1;10 versus(10 cm\ )ascanbeobservedfromFig.1aswell.Thesedefectsconsistmainlyofdislocationloops,whichimpliesthatthedefectsremainlocatedattheinterface.Whendepositingona60%porouslayer,ahighdefectdensityhasbeenobservedinboththetopoftheepilayerandintheinterfaceregion(3.5;10 cm\ ).Thedefectsmainlyconsistofrunningdislocationsandsomestackingfaults[10].

XTEM-analysisindicatesthattheporouslayerthicknessremainsunchangedaftertheepi-growth.Howeverareductionoftheremainingporosityfrom60%to21%isderivedfromSE-modeling.Thisimpliesthatpore"llingoccurs(i.e.,depositionofSiinsidetheporouslayer).RBSanalysishasbeenappliedtocheckthisresult.

RBS-channelingexperimentsonPSrevealsthatthepresenceofaporoussurfacelayergivesrisetoanincreaseofthechanneledsignal(Fig.2a).AssumingthattheporouslayercorrespondstothisregionofenhancedchanneledsignalallowsthecalculationoftheSi-countswithinthisareaandtheratiototheSi-countsthatareexpectednormallyforanequallythickSilayerresultsinavaluefortheporosity.Inthisway,a60%porosityisderivedforthehigh-porosityporoussurfacelayer,whichagreeswellwiththevalueobtainedfromSE-analysis.ThesametypeofRBSanalysisisappliedonasamplewithaburiedPSlayer(Fig.2b).TheSi-countsfortheporous