Comparison of enhanced second harmonic generation in pyramid-like in-plane MoS2 flakes to vertically aligned MoS2 flakes

Abstract

Here, we report the comparative study of enhanced second harmonic generation using defect engineering in pyramid-like MoS2 (P-MoS2) flakes to vertically aligned MoS2 (VA-MoS2) flakes. P-MoS2 and VA-MoS2 is synthesized via the modified chemical vapor deposition technique. The second harmonic generation measurements on P-MoS2 and VA-MoS2 are performed by sweeping the excitation wavelength from 1200 nm to 1310 nm in identical conditions. The P-MoS2 flakes show a high SHG signal. The high SHG signal in pyramid-like MoS2 is attributed to the broken inversion symmetry and high thickness of grown MoS2 flakes. VA-MoS2 flakes under the identical conditions show a 34% enhanced SHG signal in comparison to P-MoS2. The midgap states generated due to defects in the form of S vacancies in VA-MoS2 are responsible for this enhancement. These midgap states confine the photons and result in enhanced SHG properties. Our study will pave a new path to understand the role of 2D material morphology in fabricating versatile optical and photonics devices.

Second Harmonic Generation Control in 2D Layered Materials: Status and Outlook

“…[29,62,73,[86][87][88][221][222][223][224] 2DLMs provide an ideal platform to realize their desired nonlinear optical properties at the atomic level by stacking them in various configurations, including homo-and heterostructures with different stacking order or angle, and special grown structures like spiral and pyramid layers. [225][226][227][228][229][230][231][232][233] Tunable nonlinear optical properties of 2DLMs heavily depend on their phase, thickness, and layer stacking. [24,67,123] Especially, artificial stacking order can effectively control the overall symmetry of 2DLMs with homobilayers and thus enable us to control the SHG as desired.…”

“…By accurately controlling the growth parameters, special spiral or pyramid structures with broken inversion symmetry can be obtained. [225][226][227][228][229][230][231][232][233] Ouyang et al developed a defect-induced CVD method to obtain noncentrosymmetric stacking edge-rich spiral MoTe 2 with 3R-like structure (Figure 3g), [230] showing a remarkably enhanced SHG of three orders of magnitude as compared with monolayer MoS 2 and MoTe 2 . They attributed it to the synergistic effect of broken inversion symmetry, exciton resonance, and strong light-matter interaction caused by edge-rich structure.…”

“…[ 29,62,73,86–88,221–224 ] 2DLMs provide an ideal platform to realize their desired nonlinear optical properties at the atomic level by stacking them in various configurations, including homo‐ and heterostructures with different stacking order or angle, and special grown structures like spiral and pyramid layers. [ 225–233 ]…”

“…By accurately controlling the growth parameters, special spiral or pyramid structures with broken inversion symmetry can be obtained. [ 225–233 ] Ouyang et al. developed a defect‐induced CVD method to obtain noncentrosymmetric stacking edge‐rich spiral MoTe 2 with 3R‐like structure (Figure 3g), [ 230 ] showing a remarkably enhanced SHG of three orders of magnitude as compared with monolayer MoS 2 and MoTe 2 .…”

A strategic review of recent progress, prospects and challenges of MoS2-based photodetectors

“…Defects in MoS 2 have a great impact on electrical, optical and structural properties and play an important role in device performance [149,150]. Defects are generally induced during synthesis and transfer processes, which are unavoidable and difficult to control.…”