Ultrafast control of exciton dynamics by optically-induced thermionic carrier injection in a metal-semiconductor heterojunction

Interface effects in metals-semiconductors heterojunctions are subject of intense research due to the possibility to exploit the synergy between their electronic and optical properties in next-generation opto-electronic devices. In this framework, understanding the carrier dynamics at the metal-semiconductor interface, as well as achieving a coherent control of charge and energy transfer in metal-semiconductor heterostructures, are crucial and yet quite unexplored aspects. Here, we experimentally show that thermionically injected carriers from a gold substrate can drastically affect the dynamics of excited carriers in bulk WS2. By employing a pump-push-probe scheme, where a push pulse excites direct transitions in the WS2, and another delayed pump pulse induces thermionic injection of carriers from the gold substrate into the semiconductor, we can control both the formation and annihilation of excitons. Our findings might foster the development of novel opto-electronic approaches to control charge dynamics using light at ultrafast timescales.