Page - 154 - in Photovoltaic Materials and Electronic Devices

Table 2. Electrical and optical parameters of ITO films deposited under various oxygencompositionsandetchedfor1,3,5and8min. OxygenFlow Rate (sccm) EtchingTime (min) SheetResistance (Ω/square) Thickness (nm) Resistivity (Ω¨cm) Transmission (%) 0 1 83.28 70 5.83ˆ10´4 76.29 3 103.47 59 6.11ˆ10´4 93.98 5 209.49 44 9.22ˆ10´4 90.27 8 – – – 100 0.4 1 209.02 89 1.86ˆ10´3 91.45 3 194.23 88 1.71ˆ10´3 85.26 5 240.08 85 2.04ˆ10´3 84.85 8 326.9 47 1.54ˆ10´3 83.71 1.0 1 1000 84 8.4ˆ10´3 90.96 3 2000 62 1.24ˆ10´2 89.25 5 2400 50 1.20ˆ10´2 100 8 7350 22 1.62ˆ10´2 100 From the obtained results, the minimum sheet resistance was observed for ITO deposited using argon ambient (0 sccm oxygen) and etched for 1 min. However, the same films exhibited the worst transmittance of about 76%. During processing in an argon rich environment, the bombardment by argon neutrals creates dangling bonds in thesubstratesandcreatedtheoxygenvacancies in theITOfilms[46]. Theargon environment (10 sccm) (i.e., the oxygen deficient environment) promotes oxygen vacancies thatenhanceelectrical resistivitywhiledegradingtheopticalproperties of the films. This is reflected in the XRD spectra, where the (400) and (440) lattice planes are enhanced for ITO films processed in low oxygen (0 sccm and 0.4 sccm) environments. Hence, the1.0sccmdepositedfilmsinwhichthe (222) latticeplane isdominant, showedahigherelectrical resistivitycomparedto theotherfilms. The resistivityof thefilmsarehighlydependentonthefilmthickness,whichisa function of theetchingtime. Increasingtheetchingtimedecreases the thicknessof thefilms, and,hence, theelectricalpropertieswhile improvingopticalproperties. 3.3. Transmittance Optical transmittancesoftheITOfilmsonglasssubstratesarerecordedfrom300 to1000nmatroomtemperatureandshowninFigure2. All thefilmsexhibitedthe highestaverageoptical transmittance in thehigherwavelengthrange. Thehighest optical transmittanceisattainedfor0sccmoxygenITOfilmetchedfor8minwithand averageetch rateof 5.2nm/min(for 5minetch) andthe 1.0sccmfilms etchedfor 5 and 8 min with average etch rates of 5.25 and 7.75 nm/min, respectively. The results aresummarizedinTable2. Thethicknessof thefilmisan importantparameter for determining both electrical and optical properties of the ITO films. In this work, the thickness was quantified using spectroscopic ellipsometry measurements and is shownintheTable2. For transmittancemeasurements, the ITOfilmsweredeposited 154