Effect of Si₃N₄ Thickness on the Optical Characterization of Graphene

Optical detection of graphene on a specific substrate is important for the analysis of the physical or chemical properties of graphene. Si₃N₄, an oxygen free substrate with high dielectric constant, is a good candidate to replace SiO₂. In this letter, we report the optimization of the Si₃N₄ thickness for efficient optical characterization by means of the contrast, enhancement factor (F), and the Raman spectra of the graphene obtained on the selected Si₃N₄/Si substrate. The contrast (visibility) and enhancement factors (F, Raman intensity) of the graphene/Si₃N₄/Si structure were calculated as a function of the Si₃N₄ thickness and the wavelength of the excitation source. A suitable Si₃N₄ thickness generating high visibility and Raman intensities at the wavelength of the excitation source, 633 nm, was obtained.