Nanometric Ge Films for Ultrafast Modulation of THz Waves with Flexible Metasurface

Abstract Harnessing confined light on a subwavelength scale within Fano metasurfaces enhances light‐matter interaction on a flexible, low‐loss substrate. This approach enables the integration of ultra‐thin semiconducting films for designing low‐power, ultrafast switchable terahertz, and optical meta devices. Here, an ultra‐thin, ∼λ/6000 germanium overlayers of 25nm or 50nm is thermally evaporated onto a flexible Fano metallic metasurface to achieve ultrafast optical modulation of terahertz radiation. A remarkable 85% modulation depth with an ultrafast speed of 400 GHz is obtained in the resonant transmission. These ultrathin, flexible, and ultrafast functional metasurfaces pave the way for developing flexible terahertz active meta devices based on nanometric scale germanium films, offering the additional advantage of compatibility with complementary metal‐oxide‐semiconductor (CMOS) technology in microelectronics.