Graphene is a one-atom-thick planar sheet of a honeycomb carbon crystal. Its gapless and linear energy spectra of electrons and holes lead to nontrivial features such as giant carrier mobility and broadband flat optical response. In this paper, recent advances in graphene-based devices in terahertz science and technology are reviewed. First, the fundamental basis of the optoelectronic properties of graphene is introduced. Second, synthesis and crystallographic characterization of graphene material are described, particularly focused on the authors' original heteroepitaxial graphene-on-silicon technology. Third, nonequilibrium carrier relaxation and recombination dynamics in optically or electrically pumped graphene are described to introduce a possibility of negative-dynamic conductivity in a wide terahertz range. Fourth, recent theoretical advances towards the creation of current-injection graphene terahertz lasers are described. Fifth, the unique terahertz dynamics of the two-dimensional plasmons in graphene are described. Finally, the advantages of graphene devices for terahertz applications are summarized.

By forming an ultrathin (∼100 nm) SiC film on Si substrates and by annealing it at ∼1500 K in vacuo, few-layer graphene is formed on Si substrates. Graphene grows on three major low-index surfaces: (1 1 1), (1 0 0) and (1 1 0), allowing us to tune its electronic properties by controlling the crystallographic orientation of the substrate. This graphene on silicon (GOS) technology thus paves the way to industrialization of this new material with inherent excellence. With its feasibility in Si technology, GOS is one of the most promising candidates as a material for Beyond CMOS technology.

With its industrial adaptability, epitaxial graphene (EG), formed by a UHV annealing of SiC substrates, is attracting recent attention. While hexagonal SiC bulk substrates have been solely used for this purpose, benefits in use of 3C-SiC virtual substrate founded on Si substrates could be enormous. We have succeeded in fabricating a graphene film on a 3C-SiC(111) virtual substrate, which was preformed on a Si(110) substrate by gas-source molecular beam epitaxy using monomethyl silane. The geometrical matching in this configuration greatly suppresses the strain in the SiC film, which is related to this successful formation of graphene.

The adsorption of CO2 molecules on monolayer epitaxial graphene on a SiC(0001) surface at 30 K was investigated by temperature-programmed desorption and X-ray photoelectron spectroscopy. The desorption energy of CO2 on graphene was determined to be (30.1–25.1) ± 1.5 kJ/mol at low coverages and approached the sublimation energy of dry ice (27–25 kJ/mol) with increasing the coverage. The adsorption of CO2 on graphene was thus categorized into physisorption, which was further supported by the binding energies of CO2 in core-level spectra. The adsorption states of CO2 on graphene were theoretically examined by means of the van der Waals density functional (vdW-DF) method that includes nonlocal correlation. The experimental desorption energy was successfully reproduced with high accuracy using vdW-DF calculations; the optB86b-vdW functional was found to be most appropriate to reproduce the desorption energy in the present system.