Aluminum doped ZnO thin films deposited by direct current sputtering: Structural and optical properties

• Al-doped ZnO thin films were deposited by DC sputtering at various substrate temperatures Ts.
• AZO thin films were well crystallized in hexagonal wurtzite structure with a preferential orientation along the c-axis.
• All films exhibit a high optical transmittance in the Vis–NIR ranges and a high absorption in the UV range.
• Enhancement of the crystalline quality and the optical properties of AZO thin films with increasing Ts.
• Enhancement of electrical properties of AZO with the increase of Ts.

Direct current sputtering was used to growth Al-doped ZnO (AZO) thin films at various substrate temperatures. Structural and optical properties of AZO thin films were investigated by X-ray diffraction (XRD), energy dispersive X-ray (EDX) and Ultraviolet–Visible–Near IR spectroscopy. According to the XRD patterns, all films showed an hexagonal wurtzite structure with a preferred orientation along c-axis. EDX showed that all films are doped with 1% wt of Al. The transmittance and reflectance changed with the substrate temperature Ts. AZO has a high transmittance which is a crucial parameter for optical materials and applications. Thus, it is important to determine optical constants of the films. In this order, optical parameters such as the optical band gap, absorption coefficient, extinction coefficient, refractive index, dispersion parameter, dielectric constants and optical conductivity were studied in order to investigate the effects of Ts on the optical properties of AZO thin films. The dispersion energy, single-oscillator strength and the long wavelength refractive index of the AZO thin films were found to be affected by substrate temperature Ts.