Electronic properties of graphene (carbon) nanoribbons are studied and compared to those of carbon nanotubes. The nanoribbons are found to have qualitatively similar electron band structure which depends on chirality but with a significantly narrower band gap. The low- and high-field mobilities of the nanoribbons are evaluated and found to be higher than those of carbon nanotubes for the same unit cell but lower at matched band gap or carrier concentration. Due to the inverse relationship between mobility and band gap, it is concluded that graphene nanoribbons operated as field-effect transistors must have band gaps <0.5eV to achieve mobilities significantly higher than those of silicon and thus may be better suited for low power applications.

We present nonlocal empirical pseudopotential calculations for SiGe alloys employing a novel nonlinear interpolation scheme. Our interpolation scheme is able to correctly model for the first time the band gap bowing observed in relaxed SiGe alloys. The valence-band-edge and conduction-band-edge energies in relaxed Si1−xGex for arbitrary x, which are difficult to obtain by experimental techniques, have been evaluated using pseudopotential calculations. We have also calculated the band energies of pseudomorphic [100]-strained Si1−xGex alloys grown over unstrained Si1−yGey substrates. The energy gaps, valence and conduction band offsets, effective masses, and strain induced splittings in pseudomorphic SiGe layers are calculated for the whole range of alloy compositions x and y.

Ultrathin double-gate silicon-on-insulator transistors are studied in the quantum coherent limit. By treating electron-electron interaction on the level of a mean field approach, the density matrix of the device becomes diagonal when expressed in a basis that results from imposing scattering boundary conditions at the terminals. The self-consistent scattering wave functions are computed using a multisubband scattering matrix formalism. This allows us to retain the full dimensionality of the wave functions and eliminates the need for the adiabatic decomposition of the Schrödinger equation. Subband mixing is fully taken into account and a piecewise analytical representation of the wave functions can significantly reduce the number of sampling positions along transport direction. By self-consistent simulations the size of source-to-drain tunneling as a function of gate length is demonstrated for different body thicknesses. A strong forward bias is shown to increase the tunnel current due to the thinning of the source-drain potential barrier. The effect of channel orientation on the tunnel current is also discussed.

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We present integrated simulation of spin-transfer torque (STT) devices within the framework of a general purpose TCAD device simulator. A fast Airy function based approach is used to calculate spin and charge transport through magnetic tunnel junctions (MTJ). This enables direct mixed mode simulation of STT devices in a circuit environment -consisting of physical TCAD device models, SPICE-like compact models or a combination thereof -without first constructing a response surface model for the STT device. This was used to simulate a 4T-2MTJ non-volatile SRAM cell. For device interactions that are not captured in a circuit picture, STT and conventional devices may be combined in a single simulation geometry. Using an explicit exchange term in the Landau-Lifshitz-Gilbert equation allows capturing some aspects of spin dynamics beyond the macro-spin approximation.