Smith-Purcell Radiation from Highly Mobile Carriers in 2D Quantum Materials

Terahertz (THz) radiation has broad applications ranging from medical imaging to spectroscopy. One viable source of high-intensity THz radiation is the Smith-Purcell (SP) effect, which involves charge carriers moving over a periodic surface. Conventional SP emitters use electron beams to generate charge carriers, necessitating bulky electron acceleration stages. Here, a compact design for generating THz SP radiation using mobile charge carriers within 2D materials is proposed. This circumvents the beam alignment and beam divergence challenge, allowing for a reduction in the electron-grating separation from tens of nm to 5 nm or less, leading to more efficient near-field excitation and a potentially chip-level THz source. In such a configuration, it is shown that the optimal electron velocity and the corresponding maximum radiation intensity can be predicted from the electron-grating separation. The numerical demonstration shows that hot electrons can excite SP radiation in graphene on a silicon grating, and the radiation intensity can be increased by graphene surface plasmons. This study can be extended to a broad variety of charge carriers in 2D materials, thus allowing for compact, tunable, and low-cost THz sources.