The electron behavior in nanometer semiconductor structures is a result of complicated interplay between coherent quantum effects and processes of decoherence due to interactions with the lattice. These mixed mode transport conditions are in the research focus of FWF Project P21685, 'Wigner-Boltzmann Particle Simulations'. The basic aim of the research is to develop WIENS - a union of theoretical transport models together with corresponding numerical approaches and algorithms for particle simulation, and their applications.
The work on WIENS continues to address theoretical issues related to the Wigner formulation of quantum mechanics, the relationship between the equations of an hierarchy of transport models defined in the phase space, and to the Wigner-Boltzmann equation, which is relevant for the rich-of-phenomena semiconductor world characterized by the nanometer-picosecond-scales. The magnitudes of the components of the physical system Hamiltonian on the properties of this equation is investigated. It is shown that the increased coupling with the environment gives rise to a faster than linear suppression of the coherent terms.
The computational complexity posed by the Wigner-Boltzmann equation is already challenging in one-dimensional device simulations, and increases dramatically for more dimensions. This problem has been addressed by developing numerical schemes that allow a decomposition of a given multi-dimensional problem into a set of problems of lower dimensions, which are to be solved within iterative schemes.
Particle simulations are applied to investigate the decoherence effect of the phonons, which introduce irreversibility in the coherent electron evolution, thus causing a transition from quantum to classical behavior. They are constructed by the superposition of two wave packets initial state, which has a pronounced interference term. The latter is effectively destroyed by the phonons so that only classical components remain. Simulations evaluate the coherence life times in the picoseconds scale, which provides a physical limit for future quantum computers.