Growth of Epitaxial Graphene on 4H-SiC with Excess Electrons Provided by Electron Beam Irradiation

Abstract

Epitaxial graphene (EG) growth on a SiC substrate is one of the most intensively investigated methods for producing a graphene film in wafer-scale. The conventional EG growth done by thermal annealing in vacuum or Ar atmosphere requires heating an entire SiC substrate to very high temperature over 1300 degree C. Instead, the EG growth with electron beam (e-beam) irradiation demonstrated that the growth temperature could be lowered noticeably, below 1000 degree C [1,2]. Here, we report the controlled growth of EG on 4H-SiC(0001) substrate and the magneto-transport properties of charge carriers within it. The atomic force microscopy (AFM) images taken on the surfaces of grown EG films support the feasibility of controlling the layer number somewhat arbitrarily by adjusting the irradiation time with the e-beam current being fixed. 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 magneto-transport measurements, the electron Hall mobility is extracted to be ~994 cm2/Vs which is smaller than that of a typical mono-layer EG and matches with the surface morphological features shown in the AFM image. The most interesting observation is the negative magneto-resistance attributed to the weak localization (WL) effect arising from the quantum interference in a disordered electron system. By fitting the magneto-conductivity curve to the WL equation, a relatively short phase coherence length of ~85.57 nm is extracted, indicating the disorderness of our EG film and again matching with its surface morphology. Additionally, the density functional theory calculation shows that the irradiated electrons tend to accumulate near the surface of 4H-SiC substrate and can reduce the cohesive energy of 4H-SiC there. The reduction of cohesive energy can trigger the early sublimation of Si atoms and lower the growth temperature of EG.

[1] Go et. al., Appl. Phys. Lett. 101, 092105 (2012) [2] Jin et. al., Curr. Appl. Phys. 18, 335 (2018)