Growth of Si-incorporated TiO₂ thin films using Vapor–Liquid–Solid (VLS) method for room temperature CO₂ sensing

The current work reports the room temperature sensing of CO₂ by growing Si-incorporated TiO₂ thin films on Si-substrate with enhanced sensing response. The study suggests that the incorporation of SiO₂ in TiO₂ lattice can be used to manipulate its defect states which alter the electrical conductivity of TiO₂ from n-type to p-type. The TiO₂ and Si-incorporated TiO₂ thin films are grown on Si-substrate at 250 °C by VLS method. FESEM images confirm the formation of a continuous film and the XRD analysis of such thin films indicates transformation of crystalline anatase TiO₂ to amorphous nature upon Si incorporation. The incorporation of Si within TiO₂ also results in the formation of oxygen related vacancy states along with the reduction of Ti related vacancies within the TiO₂ lattice. Such defect states have been investigated by performing absorption spectroscopy, room temperature PL measurements and XPS analysis. The 50% Si-incorporated TiO₂ thin film is observed to provide a sensing response of 198% at 200 sccm CO₂ flow rate which is only 2.54% for TiO₂ thin film when measured at room temperature with ~ 47% relative humidity. However, such room temperature sensing response decreases with the increase of relative humidity and found to be 73% when the relative humidity is increased to 85%. Furthermore, such Si-incorporated TiO₂ sensors exhibit a fast response and recovery time of 5.7 s and 3.6 s, respectively. Therefore, the 50% Si-incorporated TiO₂ thin film-based sensors can be efficiently used for room temperature CO₂ sensing by utilizing a simple cost-effective fabrication technique.