Comparison of epitaxial graphene on Si-face and C-face 4H SiC formed by ultrahigh vacuum and RF furnace production.

We present X-ray photoelectron spectroscopy, van der Pauw Hall mobilities, low-temperature far-infrared magneto transmission (FIR-MT), and atomic force microscopy (AFM) results from graphene films produced by radiative heating in an ultrahigh vacuum (UHV) chamber or produced by radio frequency (RF) furnace annealing in a high vacuum chemical vapor deposition system on Si- and C-face 4H SiC substrates at 1200-1600 degrees C. Although the vacuum level and heating methods are different, graphene films produced by the two methods are chemically similar with the RF furnace annealing typically producing thicker graphene films than UHV. We observe, however, that the formation of graphene on the two faces is different with the thicker graphene films on the C-face RF samples having higher mobility. The FIR-MT showed a 0(-1) --> 1(0) Landau level transition with a square root B dependence and a line width consistent with a Dirac fermion with a mobility >250,000 cm(2) x V(-1) x s(-1) at 4.2 K in a C-face RF sample having a Hall-effect carrier mobility of 425 cm(2) x V(-1) x s(-1) at 300 K. AFM shows that graphene grows continuously over the varying morphology of both Si and C-face substrates.