Growth, characterization, and investigation of H₂ gas sensing performance of Al-doped ZnO thin films synthesized by plasma focus device

This paper reports characterization of Al-doped ZnO (AZO) thin films deposited on glass substrates at room temperature by a low energy (1.3 kJ) plasma focus device using a ZnO target with an Al content of 3wt%. A particular focus of investigation is on properties relevant to the usage of thin films as hydrogen gas sensors. Indeed, the dependence of angular position of substrate on structural, morphological and gas sensing properties of AZO thin films is investigated. The results obtained from X-ray diffraction (XRD) reveal that all the films are of polycrystalline zinc oxide in nature, possessing hexagonal wurtzite structure. Also XRD results indicate strong dependence of crystallinity of deposited thin films on angular position of samples. Scanning electron microscopy and atomic force microscopy results reveal the structure growth and enhancement of surface roughness with decreasing the angle with respect to anode axis. The experiments and measurements involving the AZO deposited thin films towards hydrogen were carried out at different operating temperatures within 150–400 °C for various concentrations of hydrogen in air. The H₂ sensing response enhanced with concentration and operating temperature, and reached its maximum at 300 °C to 1000 ppm concentration of hydrogen gas. The results also indicated shorter response times for samples deposited at larger angular positions.