Characterization and NO2 gas sensing performance of CdO:In2O3 polycrystalline thin films prepared by spray pyrolysis technique

Abstract

Polycrystalline CdO:In 2 O 3 thin films for gas sensor applications were prepared on glass and silicon substrates by using one-step spray pyrolysis technique from the aqueous solution of CdCl 2 and InCl 3 at a substrate temperature of 300 °C. The structure, surface morphology, and the optoelectronic properties of prepared films were characterized respectively by means of X-ray diffraction (XRD), atomic force microscope and UV-visible spectroscopy. Based on the XRD results, the polycrystalline nature of CdO films has been confirmed, and In 2 O 3 films were found to exhibit a preferred orientation along (222) diffracted plane. The grain size varies between 9.0 and 28.4 nm. The results of Hall effect measurement of CdO:In 2 O 3 thin films confirms that all films were an n-type semiconductor. The electrical properties of prepared thin films and their sensitivity to nitrogen dioxide (NO 2) gas are also studied. The influence of the operating temperature and In 2 O 3 concentration on the NO 2 response were investigated. It is found that all films are sensitive to NO 2 gas, and the ideal operating temperature for the film contented 20 vol% of In 2 O 3 was found to be 200 °C at a gas concentration of 25 ppm. The sensing mechanism of the CdO:In 2 O 3 thin film is discussed and attributed to electron transfer between the sensing element and NO 2 molecules.

Preparation and Characterization of In2O3-CuO Nanocomposite Thin Films as NH3 Gas Sensor

“…The shape of the grains changes from spherical and elliptical at 10 % copper oxide to spherical at 20 % copper oxide, due to the nanocomposite formation of the mixed films, as shown in figure 2. This behavior corresponds to the XRD result and an agreement with that described by Suhai et al [5] and Sofi et al [17].…”

“…The reason for the decrease in transmittance after adding copper oxide is the high absorption of copper oxide within the visible wavelengths, which corresponds to the small value of the optical energy gap. These results have good agreement with those of Mahdi et al [5]. The direct optical energy gap of the prepared films was calculated from the relationship between the energy values of the photon and 2, as shown in Figure -4.…”

“…where Ra and Rg are the electrical resistance values of the sensor in air and gas, respectively. Figures- (5,6,7) show the change in the electrical resistance of the sensor with the gas reaction time at different temperatures. Figure -5 shows the change in the electrical resistance verses time of indium oxide sensor towards NH3.…”

“…The enhanced sensing properties of the thin film's composite can be attributed to the p-n heterojunction contact between the semiconductor metal oxides [4]. Moreover, many attempts have been made to enhance the sensitivity and selectivity of the transparent metal oxide sensors by modifying the surface through adding metallic impurities and mixing different metal oxides [4][5][6][7][8][9]. Indium oxide (In 2 O 3 ) is an n-type semiconductor with a wide energy gap n (3.5-3.75 eV).…”

Synthesis and Characterization of a Nano (CdO)0.94:(In2O3) 0.06 / Si gas Sensor

“…Cadmium oxide (CdO) film is an n-type that belongs to the II -VI group, with face center cubic crystal structure (FCC) (rock-salt crystal structure) [5]. The CdO film is one of the most promising TCO semiconductors due to its high electrical conductivity and high carrier concentration, which make it useful for various applications, such as photodiodes and gas sensors [10,11]. It is well know that the electrical properties of CdO films can be improved by the movement of interstitial cadmium atoms and oxygen vacancies [12].…”