Effect of Zinc Content on the Refractive Index of Co-Sputtered Zn-Doped ITO Films

In this study, we investigated the possibility of using Zn-doped ITO film as an alternative material for conventional SiO₂ waveguides used in optical communication. The Zn-doped ITO films were deposited on quartz substrates using a combinatorial sputtering system, which yielded composition spread Zn-In-Sn-O (ZITO) films by co-sputtering two targets of ITO and ZnO. The Zn-doped ITO films deposited at room temperature exhibited an amorphous phase in the Zn content [Zn/(Zn+In+Sn)] range of 39∼54 at%. The Zn-doped ITO films deposited at low oxygen partial pressure showed resistivity below 10⁻³ Ω·cm and optical transmittance of ∼85% at 550 nm. The refractive index calculated by the Swanepoel method was found to be dependent on the Zn content in the Zn-doped ITO films. The calculated bending loss from the refractive index indicated that Zn-doped ITO could be utilized as a new waveguide material for various optical devices, such as optical splitters, wavelength division multiplexers (WDMs), optical modulators, and optical switches.