Ultrafast Excitonic Behavior in Two-Dimensional Metal- Semiconductor Heterostructure

The excitonic behavior in two-dimensional (2D) heterostructures of transition metal dichalcogenide atomic layers has attracted much attention. Here, we report, for the first time, the ultrafast behavior of charge carriers in heterostructure of metal (NbSe2) and semiconductor (WSe2) atomic layers via ultrafast spectroscopy. We observe a blue-shift of the excitedstate absorption peak in time-resolved absorption spectra with time delays in both the as-grown semiconducting WSe2 and the metal-semiconductor heterostructure. However, the heterostructure shows a clear difference in the peak position and relaxation time of its electrons. This result indicates higher excited energy states in WSe2 in the presence of the NbSe2 metallic layer contact and implies the existence of interlayer electron quenching from WSe2 to NbSe2 layers. The heterostructure shows a shorter time scale in the peak rise time compared to bare WSe2, due to interfacial defects between WSe2 and NbSe2 layers. The results offer a better understanding of the optoelectronic properties of 2D heterostructure interfaces.