Effect of annealing on properties of sputtered and nitrogen-implanted ZnO:Ga thin films

Abstract

Thin films of gallium-doped zinc oxide (ZnO:Ga) were deposited on Corning glass substrates by rf diode sputtering and then implanted with 180 keV nitrogen ions in the dose range of 1×10 15 ÷ 2×10 16 cm -2 . After the ion implantation, the films were annealed under oxygen and nitrogen ambient, at different temperatures and time, and the effect on their microstructure, type and range of conductivity, and optical properties was investigated. Post-implantation annealing at 550 °C resulted in n-type conductivity films with the highest electron concentration of 1.4×10 20 cm -3 . It was found that the annealing parameters had a profound impact on the film's properties. A p-type conductivity (a hole concentration of 2.8×10 19 cm -3 , mobility of 0.6 cm 2 /V s) was observed in a sample implanted with 1 × 10 16 cm -2 after a rapid thermal annealing (RTA) in N 2 at 400 °C. Optical transmittance of all films was >84% in the wavelength range of 390-1100 nm. The SIMS depth profile of the complex 30 NO - ions reproduces well a Gaussian profile of ion implantation. XRD patterns reveal a polycrystalline structure of N-implanted ZnO:Ga films with a c-axis preferred orientation of the crystallites. Depending on the annealing conditions, the estimated crystallite size increased 25 ÷ 42 nm and average micro-strains decreased 1.19 × 10 -2 ÷ 6.5 × 10 -3 respectively.