Raman Mapping Analysis of Graphene-Integrated Silicon Micro-Ring Resonators

Area of Science:

• Materials Science
• Optoelectronics
• Nanotechnology

Background:

• Monolayer graphene integration with silicon photonics is crucial for advanced devices.
• Understanding graphene's optoelectronic properties after transfer is essential for device performance.

Purpose of the Study:

• To investigate the structural and optoelectronic effects of graphene transfer processes onto silicon micro-ring resonators (MRRs).
• To characterize graphene doping and Fermi level shifts at the graphene-silicon interface.

Main Methods:

• Raman mapping spectroscopy was employed to analyze graphene's G and 2D bands.
• Peak positions, intensities, and asymmetry of Raman spectra were used to determine doping levels and structural changes.
• Graphene integrated on MRRs with different radii of curvature (10 μm and 20 μm) were examined.

Main Results:

• Graphene is electrically intrinsic when suspended over MRRs but moderately hole-doped when on the waveguide structure.
• Fermi level pinning at the graphene-silicon interface was observed, with an estimated Fermi level shift of ~0.2 eV and a hole concentration of ~3 × 10^12 cm^-2.
• Variations in G peak asymmetry were attributed to phonon stiffening due to doping and out-of-plane wrinkling of suspended graphene.

Conclusions:

• The transfer process induces significant doping in graphene integrated with silicon MRRs.
• Fermi level pinning at the heterogeneous interface is a key phenomenon affecting graphene's electronic properties.
• Device geometry (radius of curvature) did not measurably influence the doping level in this study.