Effects of Annealing in a Partially Reducing Atmosphere on Sputtered Al-Doped ZnO Thin Films
Aluminum-doped ZnO (AZO) films have been deposited by room-temperature radio frequency (RF) magnetron sputtering onto fused-quartz substrates using a ZnO:Al2O3 (98:2 wt.%) target. A post-deposition anneal in an N2 flow has been shown to improve the electrical and optical properties of as-deposited AZO. All films were polycrystalline and exhibited a hexagonal wurtzite structure with the c-axis oriented perpendicular to the substrate. An increase in the estimated crystallite size was observed after annealing. Electrical resistivity was reduced from 3.7 × 10−3 Ω cm for as-deposited layers to 7.1 × 10−4 Ω cm for annealed films. An average optical transmittance >85% for annealed films was routinely measured. X-ray photoelectron spectroscopy measurements indicated that the surfaces of all layers investigated were oxygen deficient, and the density of oxygen vacancies was found to increase following the anneal.