Optical Duality of Molybdenum Disulfide: Metal and Semiconductor.

The two different light-matter interactions between visible and infrared light are not switchable because control mechanisms have not been elucidated so far, which restricts the effective spectral range in light-sensing devices. In this study, modulation of the effective spectral range is demonstrated using the metal-insulator transition of MoS 2 . Nondegenerate MoS 2 exhibits a photoconductive effect in detecting visible light. In contrast, degenerate MoS 2 responds only to mid-infrared (not visible) light by displaying a photoinduced heating effect via free carrier absorption. Depending on the doping level, the optical behavior of MoS 2 simulates the photoconductivity of either the semiconductor or the metal, further indicating that the optical metal-insulator transition is coherent with its electrical counterpart. The electrical switchability of MoS 2 enables the development of an unprecedented and novel design optical sensor that can detect both visible and mid-IR (wavelength of 9.6 μm) ranges with a singular optoelectronic device.