Enhanced optical second-harmonic generation from the current-biased graphene/SiO2/Si(001) structure

Area of Science:

• Condensed Matter Physics
• Materials Science
• Optoelectronics

Background:

• Graphene exhibits unique optical properties due to its 2D structure.
• Second-harmonic generation (SHG) is a nonlinear optical phenomenon sensitive to material symmetry.
• Graphene on silicon dioxide/silicon (SiO2/Si) substrates is a key system for electronic and photonic applications.

Purpose of the Study:

• To investigate the effect of direct current (DC) electric current on optical second-harmonic generation (SHG) in graphene.
• To understand the mechanism behind current-induced SHG enhancement and phase inversion.
• To explore the role of charge trapping at the graphene/SiO2 interface.

Main Methods:

• Optical second-harmonic generation (SHG) measurements in reflection.
• Rotational anisotropy SHG analysis.
• Utilizing a chemical-vapor-deposition (CVD) graphene monolayer on a SiO2/Si(001) substrate.
• Applying direct current (DC) electric current to the graphene.

Main Results:

• DC electric current enhances SHG in graphene by approximately three times.
• Current-induced SHG exhibits a phase inversion along the lateral direction of current flow.
• Charge trapping at the graphene/SiO2 interface is identified as the source of enhancement.
• The trapped charges induce a vertical electric field, leading to electric field-induced SHG.

Conclusions:

• DC current significantly boosts SHG in graphene through interface charge trapping.
• The observed phase inversion in current-induced SHG is attributed to polarity switching of trapped charges.
• This study reveals a novel method for modulating nonlinear optical responses in 2D materials.