Epitaxial Graphene Grown on 4H-SiC with Near-Surface Excess Electrons Provided by Electron Beam Irradiation

We present the controlled growth of epitaxial graphene (EG) on semi-insulating 4H-SiC (0001) substrate using electron beam (e-beam) irradiation. The e-beam irradiation enables the sublimation of Si atoms to occur at noticeably lower temperature than conventional annealing in vacuum or Ar atmosphere, below 1000 degree C. To investigate the role of irradiated electrons in growing EG films, density functional theory calculations have been performed. The calculations revealed the accumulation of injected electrons near the 4H-SiC surface and the subsequent reduction in the cohesive energy of 4H-SiC. The structural qualities of the grown EG films were investigated using Raman spectroscopy and atomic force microscopy (AFM). The observed surface morphology evolution supports the feasibility of controlling the layer number somewhat arbitrarily by adjusting the irradiation time under sufficiently high current. The magneto-transport properties of the EG film containing the partially-grown additional layer on top of a mono-layer EG were characterized using a Hall-bar device. From the Hall effect measurement, the electron Hall mobility is estimated to be ~994 cm²/Vs, which is smaller than that of a typical mono-layer EG. In addition, negative magnetoresistance (MR) attributed to weak localization (WL) effect arising from quantum interference in disordered systems has been observed. By fitting the magneto-conductivity curve to the WL equation, a relatively short phase coherence length of ~85.57 nm is extracted. These transport properties are well correlated with the surface morphological features observed in the AFM image. Our findings demonstrate that e-beam irradiation can be an efficient pathway to activate solid-solid reactions exclusively near the surface.