Deposition and characterization of ultrathin intrinsic zinc oxide (i-ZnO) films by radio frequency (RF) sputtering for propane gas sensing application

An enhancing awareness about the hazardous gaseous environment in the domestic and industrial sectors is on the rise across the globe. Thus, the necessity to efficiently detect and monitor the potentially hazardous gases, mainly that are toxic and flammable, is widely being researched. Propane, a liquefied petroleum gas (LPG), is highly inflammable and explosive when it comes in contact with an ignition source. Therefore, it is highly important to develop an upgraded propane gas sensor that could be used in various places such as household appliances, liquid natural gas (LNG) and petrochemical industry, automobile and aerospace industry, and relevant sectors where the propane is used. In the present work, ultrathin intrinsic zinc oxide (i-ZnO) films were deposited by the radio frequency (RF) sputtering technique at various working pressures (2–8 mTorr) at constant 100 W for gas sensing applications. Thus, deposited films were characterized by various techniques such as X-ray diffractometry (XRD), field-emission scanning electron microscopy (FESEM), ultra-violet spectrophotometry (UV–Vis), and finally by a gas sensing technique for their structural, morphological, optical, and sensing characteristics. XRD pattern confirms the formation of hexagonal phase of ZnO with a preferred orientation along the (002) plane. The bandgap of the deposited films was determined to be between 3.19 and 3.21 eV as measured from UV–Vis spectra. The scanning electron micrographs revealed the formation of vertically aligned and cross-linked nanowall structures at lower working pressures. Finally, the gas sensing properties of the films were exclusively studied, at various operating temperatures (100, 200, and 300 °C), for different propane gas concentrations. The film deposited at 2 mTorr exhibited a gas sensitivity of 0.998 and almost equal to 30 s of response time and 35 s of recovery time at an operating temperature of 300 °C for the propane gas concentration of 500 ppm, which implies the potentiality of using this film as a propane gas sensor.