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.