Tantalum-doped tin oxide thin films using hollow cathode gas flow sputtering technology

In this work, the sputtering process of reactive gas flow sputtering was introduced to deposit n-type tin oxide films, and the relationship between film structure and optical and electrical properties is discussed in detail. The Ta doping effect was influenced by substrate temperature and O2 flow rate used in the sputtering process, two key parameters for optimizing and producing tin oxide films by GFS technology. Substrate temperature at 270 °C and O2 flow rate at 20 and 25 sccm could produce good quality SnO2: Ta films. Ta doping at 270 °C substrate temperature resulting in a minimum resistivity of 4.01 × 10-3 Ω cm, a significant reduction in transmittance in the infrared range, leading to higher carrier concentration in SnO2: Ta films (∼1020 cm-3) compared to SnO2 films (∼1019 cm-3). From XRD result, Ta doping increased film crystallinity with the increasing of O2 flow rate up to 25 sccm, followed by degradation beyond 25 sccm due to excess oxygen vacancies. With a higher substrate temperature, the effect of Ta doping on film electrical property is not effective, due to Ta doping works as scattering center and the composition of intermediate tin oxide was observed in tin oxide film, however, Ta doping still increased carrier concentration in SnO2:Ta films (4.54 × 1020 cm-3) compared to SnO2 films (2.29 × 1020 cm-3) at 25 sccm O2 flow rate. A higher substrate temperature could reach a lower refractive index of 1.92. The future pursuits will involve optimizing the Ta doping concentration on film structure and investigating epitaxial growth of SnO2: Ta films on crystalline substrates, capitalizing on the high plasma density and low energetic ion bombardment facilitated by GFS technology.