Interfacial Charge Transfer and Defect Engineering in the MoTe₂/Graphene Heterostructure for Tailored Carrier Kinetics and Nonlinear Absorption

Abstract The MoTe₂ and graphene heterostructure exhibits significant potential for ultrafast photonic switching owing to their ultrafast carrier dynamics, superior nonlinear saturable absorption (SA) properties, and scalable synthesis. Interfacial charge transfer (CT) in conjunction with material thickness modulation, plays a critical role in governing carrier dynamics and nonlinear SA properties. However, the underlying physical mechanisms remain largely unexplored. Here, femtosecond transient absorption spectroscopy and density functional theory (DFT) calculations are employed to elucidate that CT from MoTe₂ nanoplates to graphene effectively mitigates the hot‐phonon bottleneck effect in MoTe₂ nanoplates, leading to accelerated carrier recombination and enhanced the nonlinear absorption coefficient, increased from −625 to −1129 cm GW⁻¹. Moreover, thinner MoTe₂ nanoplates exhibit lower non‐saturable losses, quantified as 1.7% for three‐layer structures compared to 4% for fourteen‐layer counterparts, attributed to the higher defect density in thicker layers, which induces increased scattering losses. Transmission electron microscopy analysis and DFT calculations confirm an elevated density of Mo vacancies in thicker samples. These findings provide key insights into CT and defect‐mediated optical properties, aiding the design of high‐performance ultrafast optical switches.