Page - 146 - in Photovoltaic Materials and Electronic Devices

InfluenceofOxygenConcentrationonthe PerformanceofUltra-ThinRFMagnetron SputterDepositedIndiumTinOxideFilms asaTopElectrodeforPhotovoltaicDevices JephiasGwamuri,MurugesanMarikkannan, JeyanthinathMayandi, PatrickK.BowenandJoshuaM.Pearce Abstract: The opportunity for substantial efficiency enhancements of thin film hydrogenatedamorphoussilicon(a-Si:H)solarphotovoltaic(PV)cellsusingplasmonic absorbers requires ultra-thin transparent conducting oxide top electrodes with low resistivityandhightransmittancesinthevisiblerangeoftheelectromagneticspectrum. Fabricating ultra-thin indium tin oxide (ITO) films (sub-50 nm) using conventional methodshaspresentedanumberofchallenges;however,anovelmethodinvolving chemicalshavingofthicker(greaterthan80nm)RFsputterdepositedhigh-qualityITO filmshasbeendemonstrated. Thisstudyinvestigatestheeffectofoxygenconcentration ontheetchratesofRFsputterdepositedITOfilmstoprovideadetailedunderstanding of the interaction of all critical experimental parameters to help create even thinner layerstoallowformorefinelytuneplasmonicresonances. ITOfilmsweredepositedon siliconsubstrateswitha98-nm,thermallygrownoxideusingRFmagnetronsputtering withoxygenconcentrationsof0,0.4and1.0sccmandannealedat300˝Cairambient. Thenthefilmswereetchedusingacombinationofwaterandhydrochloricandnitric acids for1,3,5and8minatroomtemperature. In-betweeneachetchingprocesscycle, the films were characterized by X-ray diffraction, atomic force microscopy, Raman Spectroscopy,4-pointprobe(electricalconductivity),andvariableanglespectroscopic ellipsometry. All thefilmswerepolycrystalline innatureandhighlyorientedalong the(222)reflection. Ultra-thinITOfilmswithrecordlowresistivityvalues(as lowas 5.83ˆ10´4Ω¨cm) were obtained and high optical transparency is exhibited in the 300–1000nmwavelengthregionforall theITOfilms. Theetchrate,preferredcrystal latticegrowthplane,d-spacingandlatticedistortionwerealsoobservedtobehighly dependentonthenatureofgrowthenvironmentforRFsputterdepositedITOfilms. The structural, electrical, and optical properties of the ITO films are discussed with respect totheoxygenambientnatureandetchingtimeindetail toprovideguidance forplasmonicenhanceda-Si:HsolarPVcell fabrication. Reprinted fromMaterials. Cite as: Gwamuri, J.; Marikkannan, M.; Mayandi, J.; Bowen, P.K.; Pearce, J.M. Influence of Oxygen Concentration on the Performance of Ultra-Thin RF Magnetron Sputter Deposited Indium Tin Oxide Films as a Top ElectrodeforPhotovoltaicDevices.Materials2016,9, 63. 146