Analysis of the Optical Constants of Aluminum-doped Zinc-oxide Films by Using the Single-oscillator Model

Xiaoyong Gao, Yan Liang and Qing-Geng Lin

J. Korean Phys.Soc. 57,710 [doi: 10.3938/jkps.57.710 | PDF Download]

A group of aluminum-doped zinc oxide (AZO) films were prepared on glass substrates by direct-current reactive magnetron sputtering at substrate temperatures (Ts) ranging from 170 oC to 210 oC. The optical constants of the AZO films defined as Caughy model were fitted in terms of two-layer model by using the measured spectroscopic ellipsometric parameters. The Refractive index dispersion data below the interband absorption edge of the AZO films was analyzed by using a single oscillator model. The optical energy gap as-fitted by single-oscillator model demonstrated a blue and red shift at Ts increasing from 170 oC to 200 oC and above 200 oC, respectively. This could be attributable to the change of the free electron concentration, which was related to the change in effective Al-doping efficiency. The calculated parameterb, related to crystalline structure, indicated that the AZO films as-deposited fall into ionic class even though b had a little deviation from the ionic value. The b of the AZO film as-deposited at 200 oC largely remained in the ionic value range, indicating the minimum derivation from the wurtzite structure. It denoted the most effective Al substitute for the zinc sites. Additionally, the calculated plasma frequency hwp remained in violet region.