Titanium-Doped P-Type WO₃ Thin Films for Liquefied Petroleum Gas Detection

Gas sensors are an important part of smart homes in the era of the Internet of Things. In this work, we studied Ti-doped P-type WO₃ thin films for liquefied petroleum gas (LPG) sensors. Ti-doped tungsten oxide films were deposited on glass substrates by direct current reactive magnetron sputtering from a W-Ti alloy target at room temperature. After annealing at 450 °C in N₂ ambient for 60 min, p-type Ti-doped WO₃ was achieved for the first time. The measurement of the room temperature Hall-effect shows that the film has a resistivity of 5.223 × 10³ Ωcm, a hole concentration of 9.227 × 10¹² cm^-3, and mobility of 1.295 × 10² cm²V^-1s^-1. X-Ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses reveal that the substitution of W⁶⁺ with Ti⁴⁺ resulted in p-type conductance. The scanning electron microscope (SEM) images show that the films consist of densely packed nanoparticles. The transmittance of the p-type films is between 72% and 84% in the visible spectra and the optical bandgap is 3.28 eV. The resistance increased when the films were exposed to the reducing gas of liquefied petroleum gas, further confirming the p-type conduction of the films. The p-type films have a quick response and recovery behavior to LPG.