Incorporation of Ti3+ metal ions in chemically spray deposited CdO thin films for optoelectronic and chem-resistive based formaldehyde gas sensor applications

Abstract

The surface-microstructural dependent optoelectronic and gas sensing characteristics of Ti-doped CdO thin films spray deposited on tiny glass substrates at 300 °C were examined in depth. XRD measurements revealed the polycrystalline nature of CdO films. It also revealed that the typical crystallite size of CdO films varies between 28 and 41 nm. XPS analysis validated the oxidation status of the Cd, O, and Ti components. The Cd–O metal oxide modes of vibration are confirmed by Raman analysis at ambient temperature. Ti-dopant significantly modifies the surface microstructure of CdO thin films. The predicted optical bandgap of the Ti-doped CdO thin film varies between 2.38 and 2.47 eV. The Ti-doping of 0.75 wt% results in a high typical transparency value of 91%. With a rise in Ti-doping concentration, the charge carrier concentration and resistivity are arbitrarily altered. CdO films with 0.75 wt% Ti had a mobility of 94 cm² V⁻¹ s⁻¹. For the 0.75 wt% Ti doping, a high figure of merit (152.5 × 10⁻⁴ Ω⁻¹) is produced. The formaldehyde gas response of the 0.75 wt% Ti-doped CdO thin film is high (81%). The optical band-gap and degree of crystallinity of CdO thin films are thought to be controlled by Ti dopant.