Chapter 7 - Two-dimensional materials

Abstract

The single atomic crystal layer of transition metal dichalcogenides (TMDCs), with numerous exotic physical properties, has become a worthy successor to graphene. The TMDC undergoes an indirect to direct band gap transition when it is thinned down from bulk to single layer, due to the strong confinement. The single layer TMDCs hold large exciton binding energy and rich excitonic transition physics. The inversion symmetry breaking brings nonlinearity to the single layer TMDCs, making them good piezoelectricity and second-harmonic generation materials. Moreover, single layer TMDCs are found with nonequivalent valley degree of freedom, due to the inversion symmetry and strong spin-orbital coupling. As these materials possess unique electronic and optical properties, two-dimensional (2D) materials have attracted tremendous attention in scientific research and also play a crucial role in potential application for on-chip photonic and optoelectronic devices. In this chapter, we firstly introduce the emerging physical properties of the single-layer TMDCs. Then, we provide the discussion about 2D light-emitting diodes and 2D materials coupled with the optical cavities. Finally, the challenges and perspectives of the 2D on-chip photonic and optoelectronic devices are given.