Ultra-scaled phototransistors based on monolayer MoS₂

For decades, the fundamental diffraction limit of light has stymied scaling of optoelectronics beyond the micrometer scale. However, recent studies have shown that devices capable of capturing/directing electromagnetic waves can artificially focus incident light into sub-wavelength active areas, thus enabling applications such as photodetection and communication in defiance of the diffraction limit. Despite these advancements, the ultimate scaling limits of photodetectors have remained largely untested. Here, we present a two-dimensional (2D) monolayer molybdenum disulfide phototransistor that can reach specific detectivities greater than 10¹³ Jones and display a high dynamic range while possessing an electrical active area of only 0.0065 μm². Together, the nanoscale active area and ultra-thin-body nature of the sensing material correspond to an active volume of ∼4.23 × 10⁻⁶ μm³. These results indicate that scaling of 2D photodetectors beyond the diffraction limit has enormous potential so long as methods of focusing incident light continue to be developed/refined concurrently.