Enhanced photoresponses of an optically driven VO₂-based terahertz wave modulator near percolation threshold

We proposed and demonstrated a method to enhance photoresponses in the timescale from nanoseconds to microseconds of an all optically driven VO₂-based terahertz (THz) wave modulator by driving the initial VO₂ close to percolation threshold (via externally heating the initial VO₂ thin film near insulator-to-metal transition temperature). We experimentally realized 10-fold, 3-fold, and 3-fold improvement of photosensitivity, photoresponsivity, and optical modulation bandwidth of the VO₂-based THz wave modulator, respectively. Percolation theory, along with the macroscopic conductivity response, was used to explain the mechanism for photomodulation response enhancement. The enhanced photomodulation response is promising especially for optical modulators and photodetectors. This approach is also compatible with other optimization methods and can be further used to enhance other VO₂-based optoelectronic devices.