Ultrafast charge transfer between MoTe₂ and MoS₂ monolayers

High quality and stable electrical contact between metal and two-dimensional materials, such as transition metal dichalcogenides, is a necessary requirement that has yet to be achieved in order to successfully exploit the advantages that these materials offer to electronics and optoelectronics. MoTe₂, owing to its phase changing property, can potentially offer a solution. A recent study demonstrated that metallic phase of MoTe₂ connects its semiconducting phase with very low resistance. To utilize this property to connect other two-dimensional materials, it is important to achieve efficient charge transfer between MoTe₂ and other semiconducting materials. Using MoS₂ as an example, we report ultrafast and efficient charge transfer between MoTe₂ and MoS₂ monolayers. In the transient absorption measurements, an ultrashort pump pulse is used to selectively excite electrons in MoTe₂. The appearance of the excited electrons in the conduction band of MoS₂ is monitored by using a probe pulse that is tuned to the resonance of MoS₂. We found that electrons transfer to MoS₂ on a time scale of at most 0.3 ps. The transferred electrons give rise to a large transient absorption signal at both A-exciton and B-exciton resonances due to the screening effect. We also observed ultrafast transfer of holes from MoS₂ to MoTe₂. Our results suggest the feasibility of using MoTe₂ as a bridge material to connect MoS₂ and other transition metal dichalcogenides, and demonstrate a new transition metal dichalcogenide heterostructure involving MoTe₂, which extends the spectral range of such structures to infrared. (paper)