Various optical and electrical properties of aluminium doped zinc oxide (AZO) thin films were studied using ellipsometry, photoluminescence measurement, and spectroscopic ellipsometry. The effects of aluminum doping on the optical bandgap, refractive index, resistivity, and extinction coefficient were investigated. The study was supported by the National Science and Technology Major Project of China. The results can be useful for engineering design and applications.
Optical transmittance was found to be 78.5% in the visible range. Electrical resistivity was found to be 9.1 x 10-4 O*cm. The optical bandgap of AZO thin films was found to be 3.45 eV, which was lower than that of nominally undoped ZnO films. Moreover, the optical bandgap was found to be blue shifted. This can be attributed to the Burstein-Moss effect. The blue shift was also reflected in the optical transmission spectra.
The AZO thin film material is comparable to silicon material. It has a resonant frequency of 15.9 kHz and a thickness of 50 nm. It has a crystalline structure with a hexagonal wurtzite structure. The crystallite size is 15 to 30 nm.
XRD data showed the incorporation of Al into the ZnO lattice successfully. However, the doping level was found to increase the optical bandgap. The crystallite size was found to decrease with increasing doping level. The extinction coefficient also decreased with increasing doping level.
The doping level of Al also affects the haze value. This is attributed to a high carrier concentration. However, the haze value is higher for the nominally undoped ZnO film than for the ZnO film with Al doping.