UV-activated room temperature oxygen gas sensor based on TiO2-decorated bridging GaN nanowires

A reliable and high-performance oxygen (O2) sensor based on TiO2-decorated bridging Gallium Nitride nanowires (TiO2/GaN NWs) was fabricated, which operates under ultraviolet (UV) irradiation at room temperature (RT). The TiO2/GaN NWs were prepared by direct-bridge growth of GaN NWs across the trench of GaN coated sapphire substrate, followed by titanium (Ti) sputtering and thermal oxidation. The morphology characteristic shows that TiO2 nanoparticles (NPs) are anchored uniformly on the surface of GaN NWs. The sensors with various TiO2 film thickness (0, 2, 5, 10 nm) were measured at RT under 365 nm UV illumination with O2 concentrations varying from 1% to 25%. Experimental results show that when the TiO2 film thickness is 5 nm, the O2 response reaches its maximum and the limit of detection (LOD) as low as 0.45% O2. Moreover, the 5 nm TiO2/GaN NWs sensor were also measured under different wavelengths (lambda = 280, 365, 450 nm) UV illumination and found that the lower light wavelength, the higher O2 sensing. In addition, the sensor has excellent repeatability, selectivity and long-term stability, thus has a wide application in the field of O2 gas sensing.