Low Temperature Methanol Sensing by p-Type Nano-titania: Correlation with Defects States and Schottky Barrier Model

In this paper, sol-gel derived undoped p-type nano-titania thin films particularly aimed to detect low ppm (5-100 ppm) methanol at low temperature (75-150 degrees C) is reported. Anantase TiO2 thin film was deposited by sol-gel technique and p-type conductivity of the film was confirmed by Hall measurement. Nanocrystalline structure (12-15 nm) of the TiO2 film was confirmed by X-ray diffraction study and field emission scanning electron microscopy, respectively. Photoluminance spectroscopy and X-ray photoelectron spectroscopy were employed to characterize the defect structure. Methanol sensor study was carried for detecting the concentration range of 5 to 100 ppm in the temperature range of 75 to 150 degrees C. Highly promising sensing performance was observed at an optimum operating temperature of only 100 degrees C with 102% response magnitude (in 100 ppm methanol) and appreciably fast response and recovery time (similar to 8 and similar to 21 s, respectively). The possible mechanism behind the origin of p-type conductivity has been correlated with the defect distribution model. Detailed sensing mechanism of the p-nano-titania has been explained using Schottky barrier model.