Site-Selective Bi2Te3-FeTe2 Heterostructure as a Broadband Saturable Absorber for Ultrafast Photonics

Two-dimensional (2D) materials have unique structural and optoelectronic properties and have very important applications in energy, environment, and high-performance optoelectronic sensing. Among them, the nonlinear optical properties and related applications are hot research fields. Herein, a novel 2D Bi2Te3-FeTe2 heterostructure is successfully prepared by Fe3+ induction and site-selective overgrowth using a seed-mediated growth method. This heterostructure has a plate-satellite geometry with an open spatially separated surface. The Z-scan measurement characterizes the nonlinear transmittance of the heterostructure and proves the broadband saturation absorption behavior experimentally, which are superior to those of some mainstream 2D materials. In addition, the femtosecond-transient absorption spectra reveal an ultrashort recovery time of 1.7 ps at pump wavelength of 780 nm. By integrating the Bi2Te3-FeTe2 saturable absorber into fiber laser, a 164.7-ps pulse and a 481-fs pulse are produced at center wavelengths of 1064 and 1550 nm, respectively, which are better than that of the Bi2Te3 nanoplate-based mode-locking. A new approach for the synthesis of 2D composites with spatially separated structures is provided. It is demonstrated that the synthesized Bi2Te3-FeTe2 heterojunction can be a promising broadband nonlinear optical material in ultrafast optical applications.