Résumé
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.