Since 2008, epitaxial graphene growth has been developed in terms of homogeneity and scale by using a 1 ATM argon pressure at high temperature (>1650°C). Until now, it still remains challenging to obtain films with different and controlled characteristics such as the thickness or the doping by tuning the growth parameters. Here, we optimized the epitaxial growth of monolayer graphene (1LG) on 4H-SiC (0001) under a low argon pressure of 10 mbar. This intermediate pressure allows growing a continued 1LG in a short process ~1h30.First, we discuss the initial growth stages from buffer layer to 1LG as a function of annealing temperature (same heating rate). The combined Raman spectroscopy and atomic force microscopy analyses show that a buffer layer, fully covering the Si-face of SiC, forms as the first step of growth. Subsequently, 1LG starts to grow at step edges and continue to cover the buffer layer on terraces with a step-flow growth mechanism. Eventually, reproducible syntheses of 1LG films were achieved by this temperature-controlled growth process. Then, we investigate the structural and electronic properties of the 1LG films. The integrated intensity of G-band in Raman spectra normalized with respect to a HOPG reference, AG/AG-HOPG, of each spectrum in Raman map of our continued graphene film is very close to the experimental value reported for a 1LG, demonstrating the good homogeneity. Atomically resolved scanning tunnellingmicroscopy (STM) evidences a (6x6) superstructure, indicative of 1LG covering a reconstructed interface layer[7]. Regarding the transport measurement, quantum Hall plateau values observed in our graphene layers confirmed both continuity and thickness of the1LG film. Moreover, we estimated a hole concentration of p~10^10 - 10^11 /(cm^2) at 1.7 K in helium atmosphere. We ascribe this unusual doping type to an atmosphere contamination effect since we regain the typical n-doped graphene under vacuum by transport measurement and STM analysis.

Since 2008, epitaxial graphene growth has been developed in terms of homogeneity and scale by using a 1 ATM argon pressure at high temperature (>1650°C). Until now, it still remains challenging to obtain films with different and controlled characteristics such as the number of graphene layers or the doping by tuning the growth parameters. Here, we optimized the epitaxial growth of monolayer graphene (1LG) on 4H-SiC (0001) under a low argon pressure of 10 mbar. This intermediate pressure allows growing a continued 1LG in a short process time ~1h30. First, we discuss the initial growth stages from buffer layer (BL) to 1LG as a function of annealing temperature (same heating rate). The combined Raman spectroscopy and atomic force microscopy analyses show that a BL, fully covering the Si-face of SiC, forms as the first step of growth. Subsequently, 1LG starts to grow at step edges and continue to cover the terraces with a step-flow growth mechanism, as demonstrated. Eventually, reproducible syntheses of 1LG films were achieved by this temperature-controlled growth process. Then, we investigate the structural and electronic properties of the 1LG films. The integrated intensity of G-band in Raman spectra normalized with respect to a HOPG reference, AG/AG-HOPG, of each spectrum in Raman map of our continued graphene film is very close to the experimental value reported for a 1LG, demonstrating the good homogeneity. Atomically resolved scanning tunnelling microscopy (STM) evidences a (6x6) superstructure, indicative of 1LG covering a reconstructed interface layer. Regarding the transport measurement, quantum Hall plateau values observed in our graphene layers confirmed both continuity and thickness of the 1LG film8. Moreover, we estimated by transport measurement and STM analysis a hole concentration of pHall~10^10 - 10^11 cm^-2 at 1.7 K in helium atmosphere. We ascribe this unusual doping type to an atmosphere contamination effect since we regain the typical n-doped graphene under vacuum.

Thermal decomposition of silicon carbide (SiC) provides transfer free and wafer-scale homogeneous graphene forming on a semi-insulating substrate. Large-area monolayer graphene growth was initially developed at the atmospheric pressure (around 900 mbar) in an argon ambient and at high temperature (>1650°C). However, it remains challenging to obtain films with different and controlled characteristics such as the number of graphene layers or the doping by tuning the growth parameters. In this work, we optimized the epitaxial growth of monolayer graphene (1LG) on 4H-SiC (0001) under a low argon pressure of 10 mbar. This intermediate pressure allows growing a continued 1LG in a short process time of ~1h30. Here, we discuss the initial growth stages from buffer layer to 1LG as a function of annealing temperature (same heating rate). The combined Raman spectroscopy and atomic force microscopy (AFM) analyses show that a buffer layer, fully covering the Si-face of SiC, forms as the first step of growth (1600°C). Subsequently, 1LG starts to grow at step edges (1700°C) and continue to cover the buffer layer with a step-flow growth mechanism, as shown in the literature. Eventually, continued large-scale graphene films were achieved at 1750°C with a reproducible process. These graphene films were characterised by Raman, STM and electrical measurement. The integrated intensity of G-band in Raman spectra normalized with respect to a HOPG reference, AG/AG-HOPG, of each spectrum in Raman map is very close to the experimental value reported for a 1LG. Atomically resolved scanning tunnelling microscopy evidences a (6x6) superstructure, indicative of 1LG covering a reconstructed interface layer. Moreover, quantum Hall plateau values observed in our graphene layers confirmed both continuity and thickness of the 1LG film. The carrier density of pHall~1010 - 1011 cm-2 in 1LG films can be achieved at 1.7K in helium atmosphere. Thus, our as-grown 1LG graphene films with low p-type carrier density provide perspectives for further studies and applications on graphene.

Graphene, known as one carbon layer material, holds attractive properties due to its hexagonal lattice, also called honeycomb structure. Since the seminal work on mechanically exfoliated few layer graphene, more growth processes were explored: Chemical Vapor Deposition (CVD) on metals or on silicon carbide (SiC); chemical reduction of graphene oxides and SiC sublimation. In contrast to the other graphene growth techniques, thermal decomposition of SiC provides wafer-scale homogeneous graphene spontaneously forming on semi-insulating substrate. SiC sublimation is the most promising option to achieve the transfer free and wafer-scale graphene. Furthermore, graphene/SiC is compatible with lithography techniques for further applications; thereby epitaxial graphene on SiC is a potential candidate for nanoelectronics. Until now, monolayer graphene growth by SiC sublimation at a pressure closed to the atmospheric pressure (around 900 mbar) and at high temperature (>1650°C) is well known . However, to obtain films with different and controlled characteristics such as the number of graphene layers or the type of doping by controlling the growth parameters remains challenging. We will present the initial growth stages from buffer layer to monolayer graphene on SiC (0001) as a function of the temperature at low pressure (10 mbar). A reproducible synthesis of low p-type doped monolayer graphene was optimized (few 10^11 cm-2). The p-type doping are obtained here on the bare samples without any post-growth process such as lithography. A prototypal HTA-100 furnace developed by Annealsys Company has allowed the synthesis of these original samples. All the samples were characterized by Raman spectroscopy and Atomic Force Microscopy (AFM). In addition, transport measurements (at room temperature and low temperature with high magnetic field) were carried out in the case of continuous monolayer graphene films showing especially characteristics of Quantum Hall Effect.

Chemical vapor deposition has proved to be successful in producing graphene samples on silicon carbide (SiC) homogeneous at the centimeter scale in terms of Hall conductance quantization. Here, we report on the realization of co-planar diffusive Al/ monolayer graphene/ Al junctions on the same graphene sheet, with separations between the electrodes down to 200 nm. Robust Josephson coupling has been measured for separations not larger than 300 nm. Transport properties are reproducible on different junctions and indicate that graphene on SiC substrates is a concrete candidate to provide scalability of hybrid Josephson graphene/superconductor devices.