Optical and Structure Analysis of ZnO:Al Film

ZnO and ZnO:Al are wide-bandgap semiconductors which have many applications, mainly as transparent conducting films. Thin films of these compounds were deposited onto glass and silicon substrates by RF magnetron sputtering for the investigation of structural and optical characteristics. The XRD results show that the films present wurtzite structure. The formation of a polycrystalline film having a preferential crystallographic orientation in the plane (002) is observed in the doped samples. The Al incorporated films exhibited optical transmittance above 80% in the visible spectrum and a clear absorption band in the infrared due to free carriers. Additionally, the optical band gap around 3.48 eV is significantly above the values for the intrinsic ZnO (3.25 eV). Photoluminescence (PL) measurements showed a broad emission band in the visible region. In addition, PL emission lines at 3.32 and 3.37 eV showed up in Al incorporated films, and were related to excitonic emissions. The results show that the Burstein-Moss effect plays a central role in determining the optical characteristics of the doped material.