Effect of crystallinity on the nonlinear optical properties of indium–tin oxide thin films

Abstract

Transparent conducting oxides (TCO) materials have a significant nonlinear optical behaviors. Indium-tin oxide (ITO) is one of the most important TCO materials. In this paper, the nonlinear optical properties of Indium-tin oxide thin films are investigated. Firstly, indium-tin oxide thin films are deposited on glass substrates at a plate that has Tplate = 500oC temperature. The samples were prepared with concentrations and thickness (due to the amount of solutions) varied with molar values of [Sn/In] = 0.00927, 0.018, and 0.0371. Then, structural, electrical, and linear optical properties of the ITO thin films, by the X-ray diffraction (XRD), the Field Emission Electron Microscopy (FESEM), and the UV–Vis spectroscopy were studied. Also, The nonlinear optical properties of the ITO thin films are measured by using the Z-scan technique. Structural results show that the concentration of [Sn/In] = 0.018 leads to better crystalline growth of the ITO thin film, and the change in this concentration causes the film to grow amorphously. Also, results show that the sign of the nonlinear refractive index changes with the degree of crystallinity of the sample. The sample with better crystallinity has a positive nonlinear refractive index, and the amorphous samples have a negative nonlinear refractive index. The nonlinear absorption coefficient of all films is positive, which indicates the reverse saturation absorption (RSA) coefficient of all samples, and these can be used for laser mode-locking, power limiter/pulse smoother, energy limiter/pulse shortener.