Comparative study of amorphous indium tin oxide prepared by pulsed-DC and unbalanced RF magnetron sputtering at low power and low temperature conditions for heterojunction silicon wafer solar cell applications

Comparative study of indium tin oxide (ITO) was performed between films prepared by pulsed direct current (PDC) and radio frequency (RF) magnetron sputtering methods at low power and low temperature conditions. The best achieved film resistivity is in the range of 3-6 × 10−4 Ω cm with the highest electron carrier mobility of ∼60 cm2/V. The properties of the surface layer and the bulk material were analysed in details by means of X-ray photoelectron spectroscopy (XPS). Although there is a little difference in elemental compositions, it is revealed that the ITO's properties are directly related to the chemical bonding conditions. Owing to the fast film growth rate of PDC sputtering method, second phase Sn3O4 is formed which impedes the optical performance of the ITO films. Our observations suggest that the darkening of ITO is most likely due to the existence of Sn3O4 second phases that trapped inside of the film bulk. Besides material properties, we have demonstrated that the PDC sputtering method introduces more particle bombardment damage, while for RF sputtering the damage is mainly contributed by ultraviolet radiation emission. The major sputtering induced damage can be recovered by 15 min thermal annealing at 200 °C in air.