Al dopant-dependent third-order nonlinear optical parameters in ZnO thin films under CW Nd: YAG laser irradiation

Structural, morphological and optical properties of Al-doped ZnO thin films synthesized by the spray pyrolysis method on the FTO-coated glass substrate are investigated in this study. The measurements were carried out on a series of films with various contents of Al dopant from 0 up to 4% of Al/ZnO ratios. 2-D and 3-D atomic force microscopy images revealed that the Al content has a considerable influence on the surface morphology and roughness of thin films so that the grain size and surface roughness of the films decreased with increasing the Al contents. Room temperature PL spectra revealed UV as well as defect emission peaks which experienced a slight blue shift with Al/ZnO ratios increasing from 1 to 4%. Measurements of nonlinear optical properties of Al-doped ZnO thin films were performed using a CW Nd: YAG laser at 532 nm by the Z-scan technique. It was demonstrated that the Al-doped ZnO thin films have a negative nonlinearity can be related to the thermal effects. The optical limiting measurements confirmed that undoped and Al-doped ZnO thin films are good candidates for optical limiter devices at 532 nm wavelength of lasers. The effects of defect states on the nonlinearity of thin films are also investigated in this work.