Bilayer Graphene Grown on 4H-SiC (0001) Step-Free Mesas

Abstract

We demonstrate the first successful growth of large-area (200 × 200 μm(2)) bilayer, Bernal stacked, epitaxial graphene (EG) on atomically flat, 4H-SiC (0001) step-free mesas (SFMs) . The use of SFMs for the growth of graphene resulted in the complete elimination of surface step-bunching typically found after EG growth on conventional nominally on-axis SiC (0001) substrates. As a result heights of EG surface features are reduced by at least a factor of 50 from the heights found on conventional substrates. Evaluation of the EG across the SFM using the Raman 2D mode indicates Bernal stacking with low and uniform compressive lattice strain of only 0.05%. The uniformity of this strain is significantly improved, which is about 13-fold decrease of strain found for EG grown on conventional nominally on-axis substrates. The magnitude of the strain approaches values for stress-free exfoliated graphene flakes. Hall transport measurements on large area bilayer samples taken as a function of temperature from 4.3 to 300 K revealed an n-type carrier mobility that increased from 1170 to 1730 cm(2) V(-1) s(-1), and a corresponding sheet carrier density that decreased from 5.0 × 10(12) cm(-2) to 3.26 × 10(12) cm(-2). The transport is believed to occur predominantly through the top EG layer with the bottom layer screening the top layer from the substrate. These results demonstrate that EG synthesized on large area, perfectly flat on-axis mesa surfaces can be used to produce Bernal-stacked bilayer EG having excellent uniformity and reduced strain and provides the perfect opportunity for significant advancement of epitaxial graphene electronics technology.

Step-edge-induced resistance anisotropy in quasi-free-standing bilayer chemical vapor deposition graphene on SiC

“…Following the procedure adopted in Ref. 69, we analyze the overall quality of fitting the measured 2D band with a set of four Lorentzian curves and with a single Voigt function. An exemplary Raman spectrum within the terrace and step edge area is presented in Fig.…”

Introduction

“…On the other hand, the deformation of Dirac cones for the AAB-and sliding bilayer configurations [64,66,148] can be verified by using ARPES. The aforementioned electronic characteristics have also been confirmed in absorption [164, 166-168, 173, 174, 177], transmission [180,181], refection [136], Raman scattering and Rayleigh scattering spectroscopy [75,76,138,139,171,172,[236][237][238][239][240][241][242][243]. The evidence of Dirac cones has been observed for monolayer graphene in terms of the zero threshold frequency and the linear dependence of the intensity on the frequency.…”

New X-ray insight into oxygen intercalation in epitaxial graphene grown on 4H-SiC(0001)

“…The FWHM and the shape of the 2D Raman mode are commonly used to evaluate the number of graphene layers. 22,23 The narrow (FWHM 30-40 cm À1 ) and single Lorentzian shape of the 2D Raman mode indicates that before annealing, most of the sample area is covered by the monolayer graphene, which is represented by the blue color in Fig. 3(a).…”