Enhanced current-rectification in bilayer graphene with an electrically tuned sloped bandgap

Electronic and thermoelectric properties of atomically thin C3Si3/C and C3Ge3/C superlattices

The nanostructuring of graphene into superlattices offers the possibility of tuning both the electronic and thermal properties of graphene. Using classical and quantum mechanical calculations, we have investigated the electronic and thermoelectric properties of the atomically thin superlattice of C₃Si₃/C (C₃Ge₃/C) formed by the incorporation of Si (Ge) atoms into graphene. The bandgap and phonon thermal conductivity of C₃Si₃/C (C₃Ge₃/C) are 0.54 (0.51) eV and 15.48 (12.64) W m^-1 K^-1, respectively, while the carrier mobility of C₃Si₃/C (C₃Ge₃/C) is 1.285 × 10⁵ (1.311 × 10⁵) cm² V^-1 s^-1 at 300 K. The thermoelectric figure of merit for C₃Si₃/C (C₃Ge₃/C) can be optimized via the tuning of carrier concentration to obtain the prominent ZT value of 1.95 (2.72).

Abrupt current switching in graphene bilayer tunnel transistors enabled by van Hove singularities

In a continuous search for the energy-efficient electronic switches, a great attention is focused on tunnel field-effect transistors (TFETs) demonstrating an abrupt dependence of the source-drain current on the gate voltage. Among all TFETs, those based on one-dimensional (1D) semiconductors exhibit the steepest current switching due to the singular density of states near the band edges, though the current in 1D structures is pretty low. In this paper, we propose a TFET based on 2D graphene bilayer which demonstrates a record steep subthreshold slope enabled by van Hove singularities in the density of states near the edges of conduction and valence bands. Our simulations show the accessibility of 3.5 × 10⁴ ON/OFF current ratio with 150 mV gate voltage swing, and a maximum subthreshold slope of (20 μV/dec)⁻¹ just above the threshold. The high ON-state current of 0.8 mA/μm is enabled by a narrow (~0.3 eV) extrinsic band gap, while the smallness of the leakage current is due to an all-electrical doping of the source and drain contacts which suppresses the band tailing and trap-assisted tunneling.

Opening the band gap of graphene through silicon doping for the improved performance of graphene/GaAs heterojunction solar cells

Graphene has attracted increasing interest due to its remarkable properties. However, the zero band gap of monolayered graphene limits it's further electronic and optoelectronic applications. Herein, we have synthesized monolayered silicon-doped graphene (SiG) with large surface area using a chemical vapor deposition method. Raman and X-ray photoelectron spectroscopy measurements demonstrate that the silicon atoms are doped into graphene lattice at a doping level of 2.7-4.5 at%. Electrical measurements based on a field effect transistor indicate that the band gap of graphene has been opened via silicon doping without a clear degradation in carrier mobility, and the work function of SiG, deduced from ultraviolet photoelectron spectroscopy, was 0.13-0.25 eV larger than that of graphene. Moreover, when compared with the graphene/GaAs heterostructure, SiG/GaAs exhibits an enhanced performance. The performance of 3.4% silicon doped SiG/GaAs solar cell has been improved by 33.7% on average, which was attributed to the increased barrier height and improved interface quality. Our results suggest that silicon doping can effectively engineer the band gap of monolayered graphene and SiG has great potential in optoelectronic device applications.

Charge transport and mobility engineering in two-dimensional transition metal chalcogenide semiconductors

This review presents recent progress on charge transport properties, carrier scattering mechanisms, and carrier mobility engineering of two-dimensional transition metal chalcogenides.

High performance current and spin diode of atomic carbon chain between transversely symmetric ribbon electrodes

We demonstrate that giant current and high spin rectification ratios can be achieved in atomic carbon chain devices connected between two symmetric ferromagnetic zigzag-graphene-nanoribbon electrodes. The spin dependent transport simulation is carried out by density functional theory combined with the non-equilibrium Green's function method. It is found that the transverse symmetries of the electronic wave functions in the nanoribbons and the carbon chain are critical to the spin transport modes. In the parallel magnetization configuration of two electrodes, pure spin current is observed in both linear and nonlinear regions. However, in the antiparallel configuration, the spin-up (down) current is prohibited under the positive (negative) voltage bias, which results in a spin rectification ratio of order 10(4). When edge carbon atoms are substituted with boron atoms to suppress the edge magnetization in one of the electrodes, we obtain a diode with current rectification ratio over 10(6).

Molecular rectifiers based on donor/acceptor assemblies: effect of orientation of the components' magnetic moments

In forming donor/acceptor assemblies that act as molecular rectifiers, we have introduced magnetic organic molecules as electron-donating and electron-accepting moieties. We have oriented the magnetic moment of the donor and acceptor components separately and immobilized them (and their moments) so that the molecular assemblies that act as rectifiers could be formed with moments mutually parallel or anti-parallel to each other. We have characterized the molecular assemblies formed on an electrode with a scanning tunneling microscope tip. Such donor/acceptor assemblies with a control over the orientation of moments of the components provided unique systems to study the effect of the nature of alignment on molecular rectifiers. We have observed that the rectification ratio increased in junctions with moments of the components being parallel to each other. The improvement in the rectification ratio has been explained in terms of an efficient electron-transfer process in a moment-aligned junction between the donor and acceptor moieties.