Light emission from the layered metal 2H-TaSe${}_2$ and its potential applications

Abstract

Conventional metals, in general, do not exhibit strong photoluminescence. 2H-TaSe${}_2$ is a layered transition metal dichalcogenide that possesses metallic property with charge density wave characteristics. Here we show that 2H-TaSe${}_2$ exhibits a surprisingly strong optical absorption and photoluminescence resulting from inter-band transitions. We use this perfect combination of electrical and optical properties in several optoelectronic applications. We show a seven-fold enhancement in the photoluminescence intensity of otherwise weakly luminescent multi-layer MoS${}_2$ through non-radiative resonant energy transfer from TaSe${}_2$ transition dipoles. Using a combination of scanning photocurrent and time-resolved photoluminescence measurements, we also show that the hot electrons generated by light absorption in TaSe${}_2$ have a rather long lifetime unlike conventional metals, making TaSe${}_2$ an excellent hot electron injector. Finally, we show a vertical TaSe${}_2$/MoS${}_2$/graphene photodetector demonstrating a responsivity of $>10$ AW${}^{-1}$ at $0.1$ MHz - one of the fastest reported photodetectors using MoS${}_2$.