Effects of Al₂O₃ buffer layer and annealing on the structural and optoelectronic properties of AZO films

Transparent conductive aluminum-doped ZnO (AZO) films are deposited on glass substrates using radio frequency (rf) magnetron sputtering, with an AZO ceramic target (Al₂O₃ content is ~ 3 wt%). Before the AZO films is coated, the hydrophilicity of the surface of the glass substrate is increased by oxygen plasma etching. The grey Taguchi method is used to determine the effect of the deposition parameters on the structural and optoelectronic properties of AZO films. In the confirmation runs, using the grey Taguchi method, an improvement of 46.3% in electrical resistivity and of 1.74% in transmittance is observed. The effect of an Al₂O₃ buffer layer is also determined. When the thickness of the Al₂O₃ buffer is increased (from 50 nm to 150 nm), the intensity of the (0 0 2) peak for the AZO films increases and the peaks become sharper, the resistivity of the AZO films is decreased and the transmittance is slightly reduced. Annealing at 500 °C in a vacuum (2.0 Pa) for a period of 30 min, increases the performance of the AZO/Al₂O₃/glass to better than that for AZO/glass samples. Using a Rockwell-C hardness tester, the AZO/Al₂O₃ (50 nm)/glass film are classified as HF1, which represents good adhesive mechanical strength. The crystallinity of AZO/Al₂O₃ (50 nm)/glass samples that are annealed at 500 °C for 30 min is improved, the electrical resistivity is 9.70 × 10⁻⁴ Ω cm and the optical transmittance in the visible region is approximately 85%. The figure of merit shows that the bi-layer films have better optoelectronic performance.