Ultrafast Carrier Dynamics in 2D van der Waals CuTe2Cl Probed by Terahertz Spectroscopy.

The two-dimensional van der Waals material CuTe2Cl (CTC) has been theoretically predicted to possess exceptional charge separation, strong visible-light absorption, and robust dynamic stability, making it a promising candidate for high-performance optoelectronic devices. However, its carrier relaxation pathways and the experimental validation of these predicted properties remain underexplored. Here, we investigate the photocarrier dynamics of CTC flakes using ultrafast optical pump-terahertz probe spectroscopy at 1.55 and 3.1 eV. Sub-bandgap excitation (1.55 eV) yields three distinct relaxation components (lifetimes τ1 ≈ 2-4 ps, τ2 ≈ 17-34 ps, τ3 ≈ 418-667 ps), corresponding to ultrafast defect trapping, defect-mediated recombination, and three-carrier Auger recombination, respectively. In contrast, above-bandgap excitation (3.1 eV) suppresses the intermediate channel and accelerates Auger recombination due to enhanced absorption and reduced penetration depth, producing only τ1 and τ3. These findings provide critical insight into the carrier relaxation mechanisms of CTC, advancing its potential for next-generation optoelectronic applications.