Structural, electrical, and ellipsometric properties of nitrogen-annealed ZnO:Al films

We have investigated the effects of nitrogen annealing on the structural, electrical, and optical properties of Al-doped ZnO (ZnO:Al) thin films deposited by RF magnetron sputtering at room temperature. From the X-ray diffraction observations, films have highly crystalline structure with a c-axis preferred orientation. The most improvements in the electrical and optical properties of the ZnO:Al films were obtained by nitrogen annealing. The ZnO:Al films exhibited an average optical transmittance of 90–95% in the visible range and a sharp fundamental absorption edge. Spectroscopic ellipsometry (SE) was used to extract the optical constants of thin films. The optical characteristics of ZnO:Al films were modeled using a Tauc–Lorentz based dielectric function. The bandgap energy increased with the increases in nitrogen annealing temperature, which change in accordance with the Burstein–Moss effect, and was consistent with the observed changes in the transport properties.