Graphene on silicon: Effects of the silicon surface orientation on the work function and carrier density of graphene

Abstract

Density functional theory has been employed to study graphene on the (111), ( 100) and ( 110) surfaces of bare silicon (Si) substrates, which provide three different densities of surface atoms. There are several interesting findings. First, carbon atoms in graphene can form covalent bonds with Si atoms, when placed close enough on Si (111) and ( 100) surfaces, but not on the (110) surface. The Si (111) surface shifts the Fermi level of graphene into its conduction band, resulting in an increase of the electron density by three orders of magnitude. The work function of graphene is increased by 0.29 eV on the (111) surface, likely due to the surface dipole from the re-distribution of π-orbitals. The change in the number of available states below the Fermi level of graphene due to its interaction with the Si surface, is the main cause for the unconventional doping reported in this paper. The electron density can also be increased by eighty times on a Si (100) substrate without the shift of Fermi level, which is another clear example of the proposed novel doping mechanism. These striking effects that different orientations of a silicon substrate can have on the properties of graphene are related to the surface atom density of the substrate. These results provide valuable guidance to the growth of graphene on Si for various purposes for electronic devices.

Sensitive Characterization of the Graphene Transferred onto Varied Si Wafer Surfaces via Terahertz Emission Spectroscopy and Microscopy (TES/LTEM)

“…These charges also influence the graphene doping conditions and change the work function of graphene. When the graphene is transferred onto the Si surface after removing the native oxide layer by BHF etching, the graphene directly contacts the Hterminated Si surface, and the work function of graphene is slightly increased to around 4.61 eV [45]. With BHF etching on the Si surface, the Si-O bonds are replaced by Si-F bonds and form the F-terminated surface at first as a mid-stage.…”

Low-threshold and high-extinction-ratio optical bistability within a graphene-silicon-based perfect absorber

“…Here graphene is defined using the anisotropy refractive index model with the in-plane refractive index ni = 3 + i5.446λ/3 μm -1 and the out-of-plane refractive index no = 1, which coincides well with the conductivity model in the near-IR band 8 . The Kerr effect of silicon is described using the relationship of relative permittivity and local electric field: 2 , where εr(ω) is the relative permittivity of silicon under electric field intensity, εr0(ω) is the intrinsic relative permittivity of silicon, χ (3) is the third-order susceptibility of silicon and |Eloc| is the amplitude of local electric field. Here εr0(ω) is set to 11.56 which is the square of the silicon's refractive index, and χ (3) is set to 2.79 × 10 -18 m 2 /V 2 , according to reported researches 9, 10 .…”

“…The Kerr effect of silicon is described using the relationship of relative permittivity and local electric field: 2 , where εr(ω) is the relative permittivity of silicon under electric field intensity, εr0(ω) is the intrinsic relative permittivity of silicon, χ (3) is the third-order susceptibility of silicon and |Eloc| is the amplitude of local electric field. Here εr0(ω) is set to 11.56 which is the square of the silicon's refractive index, and χ (3) is set to 2.79 × 10 -18 m 2 /V 2 , according to reported researches 9, 10 . Figure 1.…”

“…To overcome this drawback, one of the promising methods of applying graphene to the optical field is to couple it with silicon, in order to combine the significant optical-electronic properties of the two materials. So far, graphene-silicon based devices have been successfully applied to the design and fabrication of high-performance transistors, modulators and so on [3][4][5][6] . In order to further extend the application of graphene-silicon devices in the optical-electronic field, in this work, we propose a kind of graphene-silicon-based perfect absorber possessing unique bistable characteristics and demenstrate its high-quality optical bistability in the near-IR band with numerical methods.…”