Effect of Cr-doping on third-order nonlinear optical properties of nanostructured Zn_1-xCr_xO thin films for Opto-Electronic device applications

In this work, Chromium (Cr) doped Zinc Oxide (ZnO) nano-structured thin films were deposited using ultrasonic spray pyrolysis technique on glass substrate at different concentration (0,1,3,5,10 wt%) with a substrate temperature of 350^oC. The effect of chromium on zinc oxide thin films was studied to extract the structural, optical and electrical characteristics using XRD, UV-Vis spectroscopy and Hall effect measurement instruments respectively. The work on undoped ZnO showed hexagonal wurtzite structure, with an ideal orientation of (101). The increase in strain with respect to doping concentration confirmed decrease in the crystallite size. Variation in the surface roughness on doping Cr is observed. The optical results depicted influence of Cr doping resulted in the decrease in transmittance. Band-gap (BG) obtained using Tauc’s plot was seen to vary with Cr-doping. Hall effect measurement at standard conditions observed decreases in carrier concentration, and indicating the conduction to be n-type. The study of third-order nonlinear optical characteristics, such as susceptibility χ⁽³⁾, nonlinear refractive index (NRI) (𝑛₂), and nonlinear absorption coefficient (β) was carried out. These findings suggest that the films consist of self-defocusing nonlinearity. The overall results confirmed that the structural and optical results were dependent on Cr concentration in ZnO.