Impact of aluminum doping on nonlinear absorption and ultrafast carriers dynamics of Al:CdO thin films

Al:CdO thin films with different aluminum doping concentrations were prepared via magnetron sputtering technique with various sputtering power. It is found that the band gap E_g of Al:CdO films gradually increases with the increase of Al doping concentration, while the crystallinity became poor at high doping concentration. The nonlinear absorption properties of the film were characterized by nanosecond Z-scan measurements. The Z-scan results show that the nonlinear absorption coefficient β of Al:CdO thin films could be effectively modulated by Al concentration, and the maximum of β (2 × 10⁻⁶ m/W) is achieved around 20 W sputtering power. The carrier dynamics of Al:CdO thin films were studied by femtosecond pump–probe measurements. The results show that the carrier relaxation lifetime, carriers absorption cross section and carriers refraction volume are larger in the high Al concentration film. The optical limiting properties of Al: CdO films were also studied. These results demonstrate that the Al:CdO film is a promising candidate for applications in all optical switches and laser devices.