Unveiling Defect-Dependent Nonradiative Carrier Dynamics in Few-Layer 2H-MoTe₂ by Femtosecond Mid-Infrared Spectroscopy

The electronic characteristics and phase stability of two-dimensional transition metal dichalcogenides (TMDs) are fundamentally regulated by defects. In 2H-MoTe2, this principle is most evident through tellurium (Te) vacancies, which act as key mediators in driving the semiconductor-to-metal phase transformation via their profound impact on charge carrier behavior and lattice restructuring. In this work, we systematically investigate defect-assisted nonradiative carrier dynamics in few-layer 2H-MoTe2 using femtosecond mid-infrared spectroscopy. By tailoring defect densities via high-temperature annealing and chemical etching, we identify a transient signal decay component (∼0.8 ps at 80 μJ/cm2 pump fluence) attributed to defect-mediated carrier trapping. This time scale shortens to 0.5 ps with elevated defect density and partially recovers to 0.6 ps upon defect reduction. Remarkably, defect-assisted nonradiative recombination prevails over Auger processes even under high carrier densities. Furthermore, excitation-wavelength-dependent studies reveal that midgap states induced by Te vacancies (∼0.4 eV below the conduction band) dominate carrier trapping and recombination. These findings provide foundational insights into defect-modulated carrier dynamics in MoTe2, advancing strategies to optimize TMD-based optoelectronic and phase-change devices through defect engineering.