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.