Structure, Optical and a Novel Approach to Low-Temperature Gas Sensing Using (SnO2)1–x(TiO2:Bi2O3)x Thin Films for NO2 Detection

Tin oxide: titanium oxide: bismuth oxide (SnO2)1–x(TiO2:Bi2O3)x composites with different loading ratios (0, 0.1, 0.15, 0.2, 0.25 and 0.3) have numerous new application in microelectronics, sensors, and capacitors. This work concerned with the synthesis of (SnO2)1–x(TiO2:Bi2O3)x composites as well as, thin films which were deposited on glass substrates as well as, silicon wafers by using pulsed laser deposition. The diffraction pattern confirms the anatase teteragonal phase of undoped tin oxide. It was observed some peaks related with titanium and bismuth oxides appeared at high loading ratios. Upon the transmission-spectra analysis, the undoped samples declared transmittance 60–67% in a visible spectrum, and the energy gap were found to decreases from 3.35 to 1.1 eV when loading ratio increases from 0 to 0.15 and then return to increases, this indicate that our samples are good materials used as absorber layers for photovoltaic applications. The physical quantities, like the refractive index, the extinction coefficient, and the real and imaginary dielectric constants, were determined. The results show that as the loading rises from 0 to 0.15, the refractive index and real dielectric constants becomes smaller and then grow up, while the extinction coefficient and imaginary dielectric constants change in reverse manner. The gas sensing measurements showed that the highest sensitivity (283% was obtained from (SnO2)0.7(TiO2:Bi2O3)0.3/c-Si at room temperature in the presence of NO2 with the lowest response time 22 s respectively. It seems convenient to conclude that titanium oxide : bismuth oxide codoping bring favorable optical characteristics, as well as, enhanced the sensitivity at room temperature.