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Biography
D.Sc. Dr. Mihail Nedjalkov, born in Sofia, Bulgaria received the Master degree in semiconductor physics at the Sofia University "Kl. Ohridski", a Ph.D. (Dr.) degree in Physics (1990), Habilitation (2001) and Doctor of Science (D.Sc.) degree in Mathematics (2011) at the Bulgarian Academy of Sciences (BAS). He is Associate Professor with the Institute of Information and Communication Technologies, BAS. He held visiting research positions at the University of Modena (1994), University of Frankfurt (1998), Arizona State University (2004) and mainly at the Institute for Microelectronics, TU-Vienna, supported by the following European and Austrian projects: EC Project NANOTCAD (2000-03), Österreichische Forschungsgemeinschaft MOEL 239 and 173 (2007-08), FWF (Austrian Science Fund) P13333-TEC (1998-99), P21685-N22 (2010-2014), P27214-N27(2017- date), START (2005-06), P-21685 (2009-2014), EC-FP7 Project SUPERTHEME and the current H2020 Project SUPERAID7. He has served as a lecturer at the 2004 International School of Physics "Enrico Fermi", Varenna, Italy, and has over 160 publications. His research interests include physics and modeling of classical and quantum carrier transport in semiconductor materials, devices and nanostructures, collective phenomena, theory and application of stochastic methods.
Wigner Analysis of Surface Roughness in Quantum Wires
Surface roughness is the low-field electron-mobility-limiting mechanism in confined structures. Classical (Monte Carlo) transport models describe the effect of electron interaction with surface imperfections in terms of Fermi's golden rule, characterized by the stationary (long time) limit of the interaction process, which gives rise to the energy-conserving delta function and a statistical averaging, which provides a position-independent scattering probability.
An alternative approach, which offers deep insight into
the processes governing time-dependent quantum electron dynamics in the presence of surface roughness, is based on a signed particle model, which provides an equivalent autonomous formulation of the Wigner theory.
The model retains many classical notions, such as phase space and point-like particles that drift and scatter like Boltzmann
carriers. The quantum information is carried by their positive or negative sign, which is used to evaluate the physical averages. Particles generate new couples of signed particles according to rules defined by the Wigner potential. Their inertial motion is not affected by the potential. In particular, the electric field causes no acceleration.
The signed particle model has been applied in a comparative study of quantum evolution in ideal and rough-surface wires. Identical Wigner states, centered in the source contact of the wire, are periodically injected. The governing physical process is tunneling. There are no artificial walls, which stop or reflect the particles, they are simply removed after reaching the domain boundaries.
Several effects distinguish the ideal from the surface-roughness modified evolution. While in the former case, the wave vector distribution along the wire remains unaffected during the evolution because of the y-independence of the potential, in the latter case, negative wave vector values exist, prompting quantum reflection caused by surface roughness. A second effect is the reduction of speed in the transport direction.
Our conclusions have revealed that far from equilibrium, the conditions along the wire become inhomogeneous, and that quantum confinement keeps the density away from the interface, thereby reducing the surface-roughness effect.
