Erasmus Langer
Siegfried Selberherr
Oskar Baumgartner
Markus Bina
Hajdin Ceric
Johann Cervenka
Raffaele Coppeta
Lado Filipovic
Lidija Filipovic
Wolfgang Gös
Klaus-Tibor Grasser
Hossein Karamitaheri
Hans Kosina
Hiwa Mahmoudi
Alexander Makarov
Mahdi Moradinasab
Mihail Nedjalkov
Neophytos Neophytou
Roberto Orio
Dmitry Osintsev
Mahdi Pourfath
Florian Rudolf
Franz Schanovsky
Anderson Singulani
Zlatan Stanojevic
Viktor Sverdlov
Stanislav Tyaginov
Michael Waltl
Josef Weinbub
Yannick Wimmer
Thomas Windbacher
Wolfhard Zisser

Hans Kosina
Ao.Univ.Prof. Dipl.-Ing. Dr.techn.
Hans Kosina received the Diplomingenieur degree in electrical engineering and PhD from the Technische Universität Wien in 1987 and 1992, respectively. He was with the Institute of Flexible Automation at the Technische Universität Wien for one year and then joined the Institute for Microelectronics, where he is currently an associate professor. He received the venia docendi in microelectronics in 1998. In the summer of 1993, he was a visiting scientist at Motorola Inc., Austin, Texas, and in the summer of 1999, a visiting scientist at Intel Corp., Santa Clara, California. Dr. Kosina served as a Technical Program Committee member in the IEEE International Workshop on Computational Electronics in 2003 and 2004 and was the chairman of the ''11th International Workshop on Computational Electronics'' held in Vienna in May 2006. He has served as the Associate Editor of the IEEE Transactions on Computer-Aided Design of Circuits and Systems since January 2004. His current research interests include the device modeling of semiconductor devices, nanoelectronic devices, organic semiconductors and optoelectronic devices, the development of novel Monte Carlo algorithms for classical and quantum transport problems, and computer-aided engineering in ULSI-technology.

Modeling of Nano-Structures for Electronic, Optical, and Thermoelectric Applications

Silicon NanoWires (NWs) and ultra-thin layers are promising building blocks for electronic and thermoelectric devices. Length scale and orientation provide additional degrees of freedom in engineering the electronic and thermal transport properties. We use the sp3d5s*-SO tight-binding model and Boltzmann transport theory, including all relevant scattering mechanisms, to investigate the thermoelectric properties of Si NWs. It is found that structural quantization below 10nm can severely affect the electronic properties of NWs by changing the curvature of the bands and altering degeneracies through valley and subband splitting. Specifically for p-type NWs, it was found that at large diameters, NWs oriented along the three principle orientations [100], [110] and [111], have a similar thermoelectric power factor. A large anisotropy in the thermoelectric power factor was found, however, for smaller diameters. As the diameter is scaled to 3nm, the power factor of the [111] and secondly the [110] NWs largely increases, whereas that of the [100] NWs remains low. This behavior originates from confinement-induced large curvature variations in the electronic subbands. In addition to electron transport we also investigated phonon transport in Si nanostructures. Si NWs with diameters in the range 1-10nm are considered. The lattice dynamics are modeled using the modified valence force field method, the ballistic thermal conductance is calculated using the Landauer transport formalism. The phonon group velocity and thermal conductance can vary by a factor of two depending on the geometrical features of the channel. Group velocity and thermal conductance is highest in the <110> NW and lowest in and the <111> NW. The <111> orientation is the most suitable for thermoelectric devices based on Si NWs. We also consider ultra-thin Si layers of major surface orientations {100}, {110}, {111}, and {112}. We find that the ballistic thermal conductance in the thin layers is anisotropic, with the {110}/<110> channels exhibiting the highest and the {112}/<111> channels the lowest thermal conductance. The resulting ratio is about two.
To model electronic transport in Quantum Cascade Lasers (QCL) and Quantum Cascade Detectors (QCD) we resort to the Pauli master equation. An efficient Monte Carlo (MC) simulator as part of the Vienna-Schrödinger-Poisson (VSP) simulation framework has been further enhanced. Several band structure models such as 2-band k·p or 4-band k·p can be combined with different in-plane dispersion relations used in the transport calculation. A model for stimulated emission and absorption of photons has been implemented. The simulator has been used to design and optimize the first functioning bi-functional QCL and QCD device. In mid-infrared and terahertz devices, novel types of optical guides and resonators are commonly found, such as ring cavities, micro-discs, photonic crystals, super-crystals and micro-antennas. Of particular interest are Photonic Crystal (PHC) cavities. This allows investigating the properties of a large finite PHC based on the analysis of a single unit cell. In our work a real-space approach is used. The periodicity is explicitly ensured by connecting the mesh vertices that lie on opposite surfaces of the unit cell. Thus, the unit cell can be made periodic only in certain spatial dimensions while different boundary conditions may be applied in the remaining dimensions. The real-space approach with mixed boundaries gives us the possibility to analyze PHC slabs. To capture this radiative dissipation effect we apply periodic boundary conditions in the horizontal plane and absorbing boundary conditions below and above the slab. Doing so, we obtain a complex photonic band structure which contains wavevector-dependent information about radiative losses for every PHC mode.
To model carrier transport in Graphene NanoRibbons (GNRs) the Non-Equilibrium Green's Function (NEGF) formalism and an atomistic tight-binding model have been employed. We investigate the effect of line-edge roughness using a non-perturbative approach. In this method, roughness is applied to many GNR samples using a Gaussian or exponential distribution and then ensemble averages are computed. Line-edge roughness at the two edges can have some degrees of correlation. In GNRs obtained by unzipping of carbon nanotubes the correlation coefficient between theses two edges is +1, whereas that for GNRs obtained from other methods is nearly zero. Our studies show that this correlation can play a significant role on the electronic properties of GNRs. In GNRs with un-correlated roughness, the electronic bandgap is strongly modulated by line-edge roughness.

Energy spectrum of the thermal conductance in ultra-thin Si layers of 2nm thickness at T=50K. Various surface and transport orientations are considered.

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