Al Doping Effect on Enhancement of Nonlinear Optical Absorption in Amorphous BiTe Thin Films.

Bismuth telluride (BiTe) has attracted significant attention due to its broadband ultrafast optical response and strong nonlinearity at high laser fluence in the field of optoelectronic materials. The objective of this work is to study the effect of Al doping on the structure, linear optical properties, and nonlinear optical absorption behavior of BiTe thin films. The amorphous Al-doped BiTe thin films with varying Al doping concentrations were prepared using magnetron co-sputtering. The structure and linear optical properties were characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, spectroscopic ellipsometry, and UV/Vis/NIR spectrophotometry. The third-order nonlinear optical absorption properties of Al: BiTe thin films were investigated using the open-aperture Z-scan system with a 100 fs laser pulse width at a wavelength of 800 nm and a repetition rate of 1 kHz. The results indicate that Al dopant reduces both the refractive index and extinction coefficient and induces a redshift in the optical bandgap. The optical properties of the films can be effectively modulated by varying the Al doping concentration. Compared with undoped BiTe thin films, Al-doped BiTe thin films exhibit larger nonlinear optical absorption coefficients and higher damage thresholds and maintaining high transmittance. These findings provide experimental evidence and a reliable approach for the further optimization and design of ultrafast nonlinear optical devices.