Target-to-substrate distance influenced linear and nonlinear optical properties of a-plane oriented ZnO:Al thin films.

This manuscript deals with the investigation of the impact of target-to-substrate distance on the linear and nonlinear optical properties of a-plane oriented aluminum-doped ZnO (ZnO:Al) thin films synthesized by the pulsed laser deposition (PLD) technique. X-ray diffraction studies proclaim an increment in the crystallinity with a decrement in target-to-substrate distance from 6 to 3 cm, attributed to increased thickness, decrease in stress, and defect levels in the thin films. A relaxation in the stress induces a decrease in the energy gap (3.47–3.37 eV) with a reduction in target–substrate distance from 6 to 3 cm is observed from UV–visible spectroscopic analysis. Spectroscopic ellipsometry confirms an increment in the refractive index and extinction coefficient with a decrease in target-to-substrate distance. From the Photoluminescence spectrum, the presence of low defect levels in the ZnO:Al thin films prepared at a shorter target-to-substrate distance is observed. The induced absorption (RSA) and self-defocusing process of ZnO:Al thin films are revealed by open aperture and closed aperture Z-scan measurements at 532 nm wavelength. The optical limiting behavior of all the thin films strongly suggests their applicability in optical power limiting. Thus, the present study emphasizes the optimization of the target-to-substrate distance to tailor the structural, linear, and nonlinear optical properties of the a-plane oriented ZnO:Al thin films. [ABSTRACT FROM AUTHOR]