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)(2)Cd center dot 2H(2)O as a precursor solution without or with (Ga(NO3)(3-x)center dot 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 (200) 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. (C) 2013 Elsevier B.V. All rights reserved.