Plasmon-Enhanced Photoresponse of Monolayer MoS₂ Phototransistor Integrated with Refractory Metasurfaces

Monolayer transition metal dichalcogenides (TMDs) are promising materials for applications in optoelectronic devices. However, due to the atomic-thin nature, the absorption in the monolayer TMDs has become a challenge in the access to high-performance optoelectronic devices. Unlike using the common plasmonic materials such as silver, gold, and aluminum to generate localized surface plasmon resonance (LSPR) to enhance the photoresponse of the monolayer TMDs. Here, we demonstrated 2D plasmonic phototransistors using a monolayer MoS₂ integrated with hafnium nitride (HfN) plasmonic metasurfaces. By using the designed plasmonic nanostructures via Finite-difference time-domain (FDTD) calculations, we have the ability to manipulate the coupling between exciton and surface plasmon resonance. In the reflection spectra, we observed the localized surface plasmon resonance (LSPR) of HfN metasurface could be tuned by controlling the geometry of the HfN nanodisk arrays. In this work, we designed a HfN nanodisk arrays with 430 nm in diameter and a period of 550 nm, the LSPR wavelength from the designed structure is at 667 nm (A exciton in MoS2). Hence, with the tunable LSPR in the HfN metasurfaces, we can further investigate the resonance-induced photoresponsivity of phototransistors. In the end, we will also discuss the potential applications of 2D plasmonic phototransistors based on the HfN metasurfaces.