External Bias Dependent Direct To Indirect Bandgap Transition in Graphene Nanoribbon

In this work, using self-consistent tight-binding calculations, for the first time, we show that a direct to indirect bandgap transition is possible in an armchair graphene nanoribbon by the application of an external bias along the width of the ribbon, opening up the possibility of new device applications. With the help of Dirac equation, we qualitatively explain this bandgap transition using the asymmetry in the spatial distribution of the perturbation potential produced inside the nanoribbon by the external bias. This is followed by the verification of the bandgap trends with a numerical technique using Magnus expansion of matrix exponentials. Finally, we show that the carrier effective masses possess tunable sharp characters in the vicinity of the bandgap transition points.Comment: Accepted for publication in Nano Letter

Intrinsic Limits of Subthreshold Slope in Biased Bilayer Graphene Transistor

In this work, we investigate the intrinsic limits of subthreshold slope in a dual gated bilayer graphene transistor using a coupled self-consistent Poisson-bandstructure solver. We benchmark the solver by matching the bias dependent bandgap results obtained from the solver against published experimental data. We show that the intrinsic bias dependence of the electronic structure and the self-consistent electrostatics limit the subthreshold slope obtained in such a transistor well above the Boltzmann limit of 60mV/decade at room temperature, but much below the results experimentally shown till date, indicating room for technological improvement of bilayer graphene.Comment: 10 pages, 2 figure

High On-Off Ratio Bilayer Graphene Complementary Field Effect Transistors

In this paper, we propose a novel S/D engineering for dual-gated Bilayer Graphene (BLG) Field Effect Transistor (FET) using doped semiconductors (with a bandgap) as source and drain to obtain unipolar complementary transistors. To simulate the device, a self-consistent Non-Equilibrium Green's Function (NEGF) solver has been developed and validated against published experimental data. Using the simulator, we predict an on-off ratio in excess of $10^4$ and a subthreshold slope of ~110mV/decade with excellent scalability and current saturation, for a 20nm gate length unipolar BLG FET. However, the performance of the proposed device is found to be strongly dependent on the S/D series resistance effect. The obtained results show significant improvements over existing reports, marking an important step towards bilayer graphene logic devices.Comment: 4 pages, 11 figure

A binary tunnel field effect transistor with a steep sub-threshold swing and increased ON current

A variant tunnel field effect transistor structure called the binary tunnel field effect transistor (BTFET) for low voltage and near ideal switching characteristics is proposed. The BTFET relies on a binary tunneling distance (HIGH and LOW) for its operation to achieve a steep sub-threshold swing with a predicted range of 5 mV/dec. The transition of tunneling distance from HIGH to LOW state is a step-function of the gate voltage with the threshold voltage as a transition voltage. BTFET has a high on-current due to the high gate electric field and a large tunneling cross section area. An orientation dependent non-local band-to-band tunneling model was used to analyze the DC characteristics of the device