Directly observing charge-transfer free carriers in 2D MoS2/ReSe2 monolayer heterostructure

Van der Waals heterostructures offer a new platform to engineer the properties of two-dimensional (2D) materials. Large scale heterostructures of MoS and ReSe monolayers were fabricated and fully investigated using time-resolved terahertz (THz) spectroscopy (TRTS), THz emission spectroscopy, and optical pump-probe spectroscopy (OPPS). The charge transfer (CT) time was estimated to be 170 fs by fitting the photocurrent model to the emitted THz pulse. In TRTS, free carrier dominated dynamic has been unambiguous investigated. In addition, it is found that interlayer and intralayer excitons are dominant in carrier dynamics before and after CT saturation in the OPPS. The intriguing results pave the way for further understanding the ultrafast carrier relaxation dynamics in 2D heterostructures and potential applications in opto-electronic devices.