Influence of aluminum precursor nature on the properties of AZO thin films and its potential application as oxygen sensor

Abstract

Al:ZnO (AZO) thin films were successfully deposited on pre-heated glass substrate using organic and inorganic aluminum precursors, i.e. aluminum acetylacetonate (ac) and aluminum chloride hexa-hydrate (cl), respectively. The properties of spray pyrolysis grown AZO thin films were investigated for a wide range of Al/Zn ratio (0.2–10%) before and after annealing at 320 °C in an inert nitrogen atmosphere. There was remarkable improvement in the electrical properties of the films after annealing. The electrical conductivity also improved on doping but the magnitude of improvement on using cl was 10 times more as compared to ac. Photoluminescence spectroscopy of AZO thin films revealed that the near band edge emission (NBE) remarkably improved on increasing Al/Zn ratio using cl with concomitant reduction in blue luminesce (BL) intensity in the visible region. On using ac, the BL intensity however increased while NBE emission decreased. AZO thin films possessed more than 85% average optical transmission in the visible region. Blue shift in the optical band gap was observed using both types of Al precursors. cl based Al precursor produces pyramid like structure at higher Al/Zn ratios. X-ray diffraction studies revealed that AZO thin films possess hexagonal wurtizite structure with preferred orientation along c-axis. The value of the crystallite size decreased on increase in Al/Zn ratio for both types of precursors. These thin films possess good oxygen gas sensing ability and have potential ability to be used as oxygen sensor.