Second harmonic generation in 2D layered materials

Abstract

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.

Interlayer exciton mediated second harmonic generation in bilayer MoS2

“…Previous reports on SHG in MoS 2 bilayers did not focus on exciton resonances 1,33,38,42,43,55 and hence signals from monolayers were 3 orders of magnitude higher than for bilayers in the off-resonant case. From our measurements in panels Fig.…”

“…onlinear optical spectroscopy of atomically thin crystals gives crucial insights into their physical properties and investigates potential applications 1,2 . Nonlinear optics is based on the interaction of photons within the crystal.…”

“…TMD monolayers such as MoS 2 and WSe 2 have broken inversion symmetry and show intrinsically strong SHG signals 1,33,34 . Excitons are strongly bound in these materials 35 and govern optical processes also at room temperature, contrary to the model semiconductor GaAs 10 .…”

Nonlinear spectroscopy of excitonic states in transition metal dichalcogenides

“…Second-harmonic generation (SHG) [1] is a powerful tool for studying optical properties of a variety of materials, including semiconductors [2][3][4], molecules [5], carbon nanotubes [6][7][8], and layered transition metal dichalcogenide (TMDC) structures [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. The nonlinear nature of the SHG allows probing material characteristics on a level that usually evades linear spectroscopy methods.…”

“…The SHG signal is very sensitive to electronic excitations, making it a powerful tool for studying the band structure and inter-band transitions. The SHG is a unique tool to fill the gap left by the Raman and photoluminescence spectroscopy, and it is well suited to study atomic and electronic structures of 2D layered TMDC systems [24]. Experiments with layered WSe 2 on h-BN substrates [23], WS 2 [14], MoS 2 monolayers [19] and bilayers [15], and 2D GaSe crystal [36] revealed a conventional six-leaf pattern of the SHG signal angular dependence, which is commonly employed to determine the orientation of the monolayer crystals [9-13, 22, 32].…”