Micro-Raman and micro-transmission imaging of epitaxial graphene grown on the Si and C faces of 6H-SiC

Antoine Tiberj,Philippe Godignon,Jean Camassel,Nicolas Camara

doi:10.1186/1556-276x-6-478

Abstract

Micro-Raman and micro-transmission imaging experiments have been done on epitaxial graphene grown on the C- and Si-faces of on-axis 6H-SiC substrates. On the C-face it is shown that the SiC sublimation process results in the growth of long and isolated graphene ribbons (up to 600 μm) that are strain-relaxed and lightly p-type doped. In this case, combining the results of micro-Raman spectroscopy with micro-transmission measurements, we were able to ascertain that uniform monolayer ribbons were grown and found also Bernal stacked and misoriented bilayer ribbons. On the Si-face, the situation is completely different. A full graphene coverage of the SiC surface is achieved but anisotropic growth still occurs, because of the step-bunched SiC surface reconstruction. While in the middle of reconstructed terraces thin graphene stacks (up to 5 layers) are grown, thicker graphene stripes appear at step edges. In both the cases, the strong interaction between the graphene layers and the underlying SiC substrate induces a high compressive thermal strain and n-type doping.

Highlights

Raman in 1928 [1,2], Raman spectroscopy has become increasingly popular in materials science and, especially, in semiconductor physics and microelectronics
We review some recent Raman imaging results collected on epitaxial graphene grown on the Cand Si-faces of 6H-SiC substrates [27,28,29]
Raman imaging of isolated graphene ribbons grown on the C-face In Figure 1, we show the results of a large (20 × 100 μm2) map collected on two neighboring graphene ribbons

Summary

Introduction

The relative extinction is not measurable in several cases: (i) if no bare SiC exists on the sample (for instance as graphene fully covers the SiC surface), (ii) if impurities (dust) or metal contacts cover the graphene and/or the SiC In this particular case, we can evaluate the thickness by assuming that the average G band normalized intensity of a monolayer is between 0.025 and 0.03. The presence of these crystalline silicon (c-Si) clusters is evidenced by the sharp and intense band around 532 cm-1 blue shifted compared to bulk silicon. There might be a link between the presence of different defects at the step edges like these clusters, the higher growth rate and the clear electrical anisotropy that has been evidenced by magnetoresistance experiments performed on several Hall bars with different orientations [29]

Conclusions

14. De Wolf I

24. Ferralis N

35. Casiraghi C