Study on structural and optical properties of Mn-doped ZnO thin films by sol-gel method

For ZnO, doping transition metal is one of the powerful tools to improve its photoelectric performance. In this study, Mn-doped ZnO thin films with various thickness and different doping concentration were synthesized by low cost sol-gel method. We systematically investigated structural and optical properties of Mn-doped ZnO with different concentrations and film thickness. Research showed that with the increase of Mn doping concentration, the crystallization of ZnO decreased, and the preferred orientation was weakened. Moreover, the ultraviolet-visible (UV-Vis) absorption coefficient rose as the energy gap (Eg) decreases and Urbach energy (E-U) increases). In the intrinsic emission region below 380 nm and in the defect emission region of 440-600 nm, Mn-doped 1.5% ZnO showed the strongest emission, then the excessive doping would reduce photoluminescence of ZnO. However, in the defect emissions region of 380-440 nm, pure ZnO showed highest emission that decreased gradually with the increase doping concentration. Meanwhile, as the increase of film thickness, the crystallization properties of ZnO were improved, but there were more cracks which resulted in the decrease of UV-vis absorption coefficient, the decrease of E-g and the increase of E-U). Meanwhile, the intrinsic emission enhanced and the defect emissions decreased.