Seite - 148 - in Photovoltaic Materials and Electronic Devices

demonstrated [38]. Building on the promise of that technique, this study seeks to further understand the effect of oxygen concentration on the etch rates of RF sputter deposited ITO films and the impact on the TCO quality as a top electrode for PV devices. A detailed understanding of the interaction of all critical parameters, which determines the quality of ultra-thin ITO will help create even thinner layers with good quality to allow more finely tuned plasmonics resonances. ITO films were deposited using four different oxygen concentrations (0 sccm, 0.4 sccm, 1.0 sccm), annealed in air at 300 ˝C for 30 min and then etched for four different times (1, 3, 5 and 8 min) to establish the effect of oxygen on etch rates. These materials were characterizedbyX-raydiffraction(XRD),atomic forcemicroscopy(AFM),Raman Spectroscopy, 4-point probe (4PP), and variable angle spectroscopic Ellipsometry (VASE). In addition, the thin films were investigated for candidates as acid-resistant TCOs for encapsulation of PV devices, which may reduce device processing steps andfabricationcostsofcompletedmodules in the future. Theresultsarepresented anddiscussed. 2. MaterialsandMethods 2.1. ITOFabricationProcess ITO films were grown on (100) prime silicon substrates with a 98 nm thermally grown oxide, and on glass substrates using a 99.99% 100 mm diameter pressed ITO (SnO2:In2O3 10:90 wt%) target. Before the deposition the substrates were ultrasonically cleaned in isopropanol and in DI water for 15 min and dried using N2 atmosphere. Thesputteringchamberwas initiatedtoa low10´7 Torrbasepressure and the pressure was maintained at 7.5ˆ10´3 Torr. The distance between the target and substrates was kept constant at 75 mm. As a standard procedure, the target waspre-sputtercleanedatapowerof150W,whereas thesputterdepositionof the films was performed at 100 W. The argon gas flow rate was fixed at 10 sccm and the oxygen gas flow was varied such as 0, 0.4 and 1.0 sccm with sputter rate of 8–12nmperminute. Thesputter ratewasseentodecreasewith increase inoxygen flow rate. After deposition, ITO films were annealed at 300 ˝C for 30 min in air. ITO/Sifilmsweresubjectedto theetchingprocessusingastandardchemicaletchant mixtureofHCl: HNO3:H2O(1:1:5)volumeratio. All theetchingwasperformedat room temperature, resulting in a slowand controlledetch rate for theSi/SiO2 films. Finally, the etched samples were thoroughly rinsed in DI water and dried under the nitrogenenvironment. Thismethodologywasadaptedfromthepreviousstudyby Gwamuri et al., 2015 [37]. TheITOfilmsprocessedunderdifferentargon-oxygenambientwerechemically etched and characterized using various tools. The structural analyses of the ITO filmswerecarriedoutusingX-raydiffraction(XRD-Scintag-2000PTS,ScintagInc., Cupertino, CA, USA). Raman spectra for the ultra-thin film samples were measured 148