Graphene is an almost ideal two-dimensional system. Unlike other two-dimensional electron gas systems realized in silicon or gallium arsenide, the electron wave functions are very close to the surrounding environment. While this causes problems in trying to passivate the surface without reducing the mobility, it does allow direct electrical access to the two-dimensional surface states using sca...

An exchange-correlation energy functional beyond the local density approximation, based on the exchange-correlation kernel of the homogeneous electron gas and originally introduced by Kohn and Sham, is considered for electronic structure calculations of semiconductors and atoms. Calculations are carried out for diamond, silicon, silicon carbide and gallium arsenide. The lattice constants and ga...

We present the design, fabrication and characterisation of an intersubband detector employing a resonant metamaterial coupling structure. The semiconductor heterostructure relies on a conventional THz quantum-cascade laser design and is operated at zero bias for the detector operation. The same active region can be used to generate or detect light depending on the bias conditions and the vertic...

We present a polarization-independent metamaterial design for the construction of electrically tunable terahertz (THz) devices. The implemented structure consists of an array of gold crosses fabricated on top of an n-doped gallium arsenide (GaAs) layer. Utilizing THz time-domain spectroscopy, we show that the electric resonance and thus the transmission properties of the cross structure can be ...

We have implemented parallel algorithms for density-functional-theory (DFT) based electronic-structure calculations. These include a plane-wave based algorithm, a real-space-grid algorithm based on a high-order finite difference method, and a linear-scaling real-space algorithm using localized orbitals. Parallelization schemes are described for these algorithms, and the computational complexity...

We measure the lasing dynamics of single and coupled photonic crystal nanocavity array lasers fabricated in the indium gallium arsenide phosphide material system. Under short optical excitation, single cavity lasers produce pulses as fast as 11 ps full width at half maximum , while coupled cavity lasers show significantly longer lasing duration which is not explained by a simple rate equation m...

We introduce two CAD tools, checkT, and minT, , for timing verification and optimal clocking. Both tools are based on a new timing model of synchronous digital circuits which is: 1) general enough to handle arbitrary multiphase clocking; 2) complete, in the sense that it captures signal propagation along short as well as long paths in the logic; 3) extensible to make it relatively easy to incor...