Vanadium dioxide for terahertz devices

We investigate VO$_{2}$ as a material for ultrafast sub-millimeter wave devices. This material exhibits a semiconductor to metal transition (SMT) at $\sim$68 $^{\circ}$C which results in a dramatic increase in carrier density ($\sim10^{19} - 10^{23}$ cm$^{-3}$). The SMT transition can be induced thermally, electrically, or optically enabling strong interactions and unique device operation. This transition has been exploited for numerous microwave/terahertz devices such as tunable filters and modulators. However due to its low carrier mobility ($\sim 0.1$ cm$^{2}$/V-s) and long recovery times ($\sim$ ns), VO$_{2}$ has been largely ignored as a possible material for millimeter wave and terahertz pulse generation even though the SMT can occur within 100 fs. VO$_{2}$ thin film devices were fabricated and characterized. These devices were capable of generating $\sim$1 ps electrical pulses. We will present details on the ultrafast switching behaviors of VO$_{2}$ along with the design and fabrication of terahertz emitter based on the SMT of VO$_{2}$.