UC San Diego

Semiconductor being the cornerstone of modern technology, has played an indispensable role in electronic and photonic devices that are widely used in both industry and commerce. Recent decades have witnessed the emergence of its two-dimensional (2D) form, i.e. monolayer or few-layer, which was found to exhibit several extraordinary properties than its bulk counterpart owing to quantum confinement. On the one hand, atomically thin semiconductors have reduced dielectric screening effect that increases the band gap and exciton binding energy, resulting in excitonic emission and absorption in the visible spectrum. Because of the strong electron-hole interaction, they are attractive candidates for optoelectronic applications such as sensors, modulators, solar cells and light emitters. On the other hand, 2D semiconductors as layered crystals offer a superb platform for stacked heterostructures that feature interlayer interactions and more intriguing physics if twisted at an angle. The lack of spatial inversion symmetry in their crystals also opens up valley degree of freedom, offering tremendous opportunities for future information processing devices. However, due to their ultra-thin thickness by nature, conventional photonic devices that function well with bulk semiconductors may not apply to these layered atoms. In this dissertation, by integrating 2D semiconductors with optical resonators, specifically photonic crystals, a substantial spatial overlap between the material and delocalized photonic resonances is achieved. The light-matter interaction is enhanced by increased excitation rate and Purcell effect; in the strong coupling regime, the interaction results in the formation of exciton-polariton, a half-light, half-matter quasiparticle. The interaction between valley-polarized excitons and polarization dependent guided resonances also enables possible valleytronic applications. Through this enhanced light-matter interaction, we are able to manipulate the light emission, absorption and scattering properties in the TMDC-based devices. We believe that these studies can help unveil the unprecedented potential of 2D semiconductors and propel them forward to next-generation photonic and optoelectronic devices with reduced sizes, improved efficiency and advanced functionality.