关于多孔硅(4)

多孔硅在太阳电池中应用有着很大的 潜力。

480R.Bilyalovetal./SolarEnergyMaterials&SolarCells65(2001)477}485

Fig.2.RBSchanneledsignalon(a)aporoussurfacelayerwith60%porosity,(b)asamplewithanepilayerontopofaburieddualporousSilayer.Incase(a)theverticallineindicatesthepointuptowheretheSi-countshavebeencalculated.Incase(b)thedashedlinecorrespondstothetheoreticalpro"leofaSilayerwithathicknessthatequalstheporousandepitaxiallayerthickness.

andepitaxiallayerapproachthevaluethatisexpectedforbulkSihavingthesamethickness.Thisimpliesastronglydecreasedporosity.HencealsoRBSindependentlyprovidesexperimentalevidencetosupportthepictureofasigni"cantlydecreasedporositywhendepositingac-Si"lmontopofhigh-porosityPS.FromFig.2b,italsofollowsthatthechanneledsignaldecreasesforhigherenergies.Thelowminimumyield(&3%)impliesthatthecrystallographicqualityoftheepilayernearthesurfaceisclosetothequalityofstandardepilayersgrownonSisubstrates.ThisisinagreementwiththeobservationsfromXTEM-analysis(Fig.1).

Suchaporositydecreaseisconsistentlyobservedforbothporoussampleshavingalowandhighinitialporosity.Aporouslayerwithaninitialporosityof60%exhibitsaremainingporosityof20}25%,whiletheinitialporosityof20%reducesto10}15%inthecaseofalow-porosityPSlayer.Thepore"llinge!ectisclaimedtobemorepronouncedforlowdepositionrates[11],whichisthecaseforthisworkwherethermalCVDisappliedinitslowertemperatureregime.

3.2.SIMSanalysis

ThegetteringpropertiesofPSarestudiedonMG-SiusingSIMSanalysis.Fig.3showsCrandCupro"leinthefollowingstructure:150nmSigrownat8003Con700nmPSwithaninitialporosityof80%formedonMG-Si.BoththeCuandCrconcentrationsarehigherwithintheporouslayer.Thismightindicateagetteringactivityoftheburiedporouslayeraswasreportedearlier[5].Ontheotherhand,the