Second harmonic generation in 2D layered materials

Second harmonic generation (SHG) of two-dimensional (2D) layered materials has attracted immense research interests due to the abilities of photon generation, manipulation, transmission, detection, and imaging for the applications of modern on-chip nanophotonic devices. Some layered materials with broken inversion symmetry associated with their 2D nature enable the development of nanophotonic and nanooptoelectronic devices based on the second harmonic generation effect. Recently, many 2D materials with broken inversion symmetry have been discovered, which not only exhibit SHG quantum effects but also greatly promote the development of nanophotonics. In this review, we review the recent developments of all 2D SHG materials, including the graphene-like family, transition metal dichalcogenides, IIIA-VIA compounds and others. We focus on their fabrication, structural characteristics, and generating mechanism and basic characteristics of SHG, associated with the main strategies to tune, modulate, and enhance the SHG of 2D materials. Additionally, several practical applications and possible future research directions of 2D material-based SHG are discussed.