Terahertz emission spectroscopy for monitoring hot-carrier transport in Plasmonics

Hot carriers –electrons and holes with energies notably larger than k­_BT_room­– play a key role in many photon-driven processes ranging from solar energy harvesting to photochemistry. In majority these applications, the transport of hot carriers across metal/dielectric interfaces is necessary. Understanding characteristic time and length scales for the interfacial transport of hot carriers is a challenging but highly rewarding task, as optimizing the performance of hot carrier devices heavily depends on such knowledge. Our experimental knowledge of the transport dynamic is limited to gathered timescales from pump-probe experiments. However, considering that generation of hot carriers is only one of many transient processes with similar timescales, often such recorded data provide an indirect picture of charge transport and require theoretically heavy modelings to unravel the contribution of transport among other competing transient effects. Here, we discuss the measurement of hot-carrier transport dynamics via the recording of time variation of emitted terahertz waveforms upon the interfacial transport of hot carriers. The role of geometrical symmetry, propagation direction of charge transport, and the external DC electrical bias on the terahertz response will be discussed.