Abstract
Raman spectroscopy is frequently used to study the properties of epitaxial graphene grown on silicon carbide (SiC). In this work, we present a confocal micro-Raman study of epitaxial graphene on SiC(0001) in top-down geometry, i.e. in a geometry where both the primary laser light beam as well as the back-scattered light is guided through the SiC substrate. Compared to the conventional top-up configuration, in which confocal micro-Raman spectra are measured from the air side, we observe a significant intensity enhancement in top-down configuration, indicating that most of the Raman-scattered light is emitted into the SiC substrate. The intensity enhancement is explained in terms of dipole radiation at a dielectric surface. The new technique opens the possibility to probe graphene layers in devices where the graphene layer is covered by non-transparent materials. We demonstrate this by measuring gate-modulated Raman spectra of a top-gated epitaxial graphene field effect device. Moreover, we show that these measurements enable us to disentangle the effects of strain and charge on the positions of the prominent Raman lines in epitaxial graphene on SiC.
Highlights
In this work we have demonstrated the possibility to probe EG layers by Raman spectroscopy in a top-down geometry, i.e. through its silicon carbide (SiC) substrate
We observed an unexpected increase in collection efficiency and explained it in terms of dipole radiation at a dielectric surface
The fact, that most scattered light of the graphene layer is emitted into the higher refractive index material provides important input to the field of Raman spectroscopy of graphene and is limited to EG on SiC because in general graphene has to reside on a substrate
Summary
Disentangling the effect of strain and charge on the position of Raman signals of epitaxial graphene In order to better understand the role of charge and strain on the Raman signals of EG on SiC we have studied how the position of the G and 2D line depends on the carrier concentration in a top-gated quasi-free standing EG transistor. The SiN gate dielectric used in the present study has recently been shown to induce an additional electron doping of the graphene layer [27].
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Published Version
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