Liquefied petroleum gas sensing properties of sprayed nanocrystalline Ga-doped CdO thin films

Undoped and Ga-doped cadmium oxide thin films were prepared by chemical spray pyrolysis technique using (CH3COO)2Cd·2H2O as a precursor solution without or with (Ga (NO3)3−x·H2O) as a doping solution, respectively. The dopant concentration (at% Ga to Cd) was varied from 0 to 2.5 at%. X-ray diffraction (XRD) analyses reveals all the films are of polycrystalline cadmium oxide, possessing cubic structure. The film shows the (2 0 0) preferential orientation for undoped CdO and Ga-doped CdO films. The crystallite size for the 1.5 at% Ga-doped film is found to be minimum (15 nm) among all the films. At a higher doping concentration of 2.5 at%, the disorder produced in the lattice causes an increase in the resistivity of the film. It is found that compared to the undoped CdO film, Ga-doped films show high response to LPG. Among all the doped films studied, the 1.5 at% Ga-doped CdO film shows the maximum response (63%) to 1040 ppm of LPG in air at 673 K. Further, the response and recovery times of the films to LPG become shorter at higher operating temperatures. A possible mechanism of LPG sensing has been explained. The photoluminiscence (PL) studies reveal UV emission in pure CdO which shifts to green emission on doping of Ga.