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

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. [ABSTRACT FROM AUTHOR]