Optically Monitored Electrical Switching in VO2

We demonstrate a hybrid silicon–vanadium dioxide (Si-VO2) electro-optic modulator that enables direct probing of both the electrically triggered semiconductor-to-metal phase transition in VO2 and the reverse transition from metal to semiconductor. By using a two-terminal in-plane VO2 electrical switch atop a single-mode silicon waveguide, the phase change can be initiated electrically and probed optically, separating the excitation and measurement processes and simplifying the analysis of the metal-to-semiconductor dynamics. We demonstrate a record switch-on time for high-speed electrical semiconductor-to-metal transition, with switching times less than 2 ns, and quantify the slower inverse transition, which is dominated by thermal dissipation and relaxation of the metallic rutile lattice to the monoclinic semiconducting phase. By limiting the current through the VO2 to reduce Joule heating, we enable inverse relaxation times as fast as 3 ns.