Composition engineering of AZO films for controlled photon-electron conversion and ultrafast nonlinear optical...

Exploring micro-nano photonic crystals as nonlinear optical switching and optical limiting devices for Gaussian light fields with ultrashort pulse widths has attracted extensive research, mainly originating from its controllable modulation of the third/fifth-order nonlinear optical behavior and ultrafast carrier dynamics. In this work, Al-doped ZnO (AZO) films with controllable and excellent third-order nonlinear optical behavior have been uniformly deposited on quartz substrates by a single-step co-sputtering method. Al dopant-dependent ultrafast carrier dynamics and nonlinear optical properties in hexagonal ZnO films are discussed. The bonding mode of Al atoms in the ZnO lattice changed from substitutional to substitutional-decoration, which has been controllably achieved at different DC sputtering powers. The strain, crystallinity, grain size, dislocation density, and texture coefficient of the sample were quantitatively calculated by XRD and Raman spectroscopy, which confirmed that the phase parameters can be regulated by the sputtering power. In addition, Hall test and photoluminescence spectra showed the contribution of the donor level on the band structure and the electron transfer characteristics, which will provide a strategy for understanding multi-type carrier dynamics under strong light fields. The finite-difference time-domain method was used to simulate the linear optical absorption/transmittance of the sample under a plane-wave optical field, which proved that the light-matter interaction failed to be significantly suppressed by shading and scattering effects. The carrier relaxation process and nonlinear absorption/refractive effects were controllably optimized by dopant Al atoms, which were confirmed by Z-scan and transient absorption spectroscopy. Compared with pure ZnO films, the third-order nonlinear refraction and absorption coefficients of AZO-power films can reach -8.926 × 10^-15 m² W^-1 and -0.634 × 10^-7 m W^-1, respectively. AZO films with ultrafast carrier dynamics and controllable excellent third-order nonlinear optical coefficients can be used as all-optical switches and optical limiting devices, which provide a reference for advanced micro-nano optical materials.