2D semiconductors have recently emerged as promising optoelectronic materials, with high quantum efficiency of photoemission, absorption and nonlinear optical properties. With significant progress in understanding the material science of these atomically thin materials, and building devices with stand-alone monolayer materials, it is an opportune time to integrate these materials with existing optoelectronic platform to realize the full potential of the 2D materials. Here, we highlight our recent progress in 2D semiconductor integrated with nanophotonic resonators. Specifically, we report the operation of an optically pumped laser, cavity enhanced electroluminescence and cavity enhanced second harmonic generation.
Electronic valleys are energy extrema of Bloch bands in momentum space. In analogy to electrons with spin degrees of freedom, valley indices can be considered as pseudo-spins for new modes of electronic and photonic device operation. In this paper, we will review our experimental progress on the investigation of these pseudo-spins using atomically thin semiconductors (MoS2, MoSe2 etc.), which are either monolayer or bilayer group VI transition metal dichalcogenides. We will show that these new 2D semiconductors not only behave as remarkable excitonic systems, but also provide an ideal platform for realizing the optical manipulation and electrical control of valley degrees of freedom.