Events at Physics |
Seungwon Lee, Fabiano Oyafuso and Gian Franco Sacco
NASA - Jet Propulsion Laboratory
California Institute of Technology
The modeling of nano-scale devices requires simulation capabilities at length scales that span many orders of magnitude, precluding the use of a single modeling approach. At one end, the electrodes have significant features at the micron scale, and at the other end, the electronic wavefunctions are defined at the sub-nanometer scale. We have been integrating a hierarchy of approaches, for the calculation of the electronic structure and the lattice dynamics, into a package that can for example compute the effect of varying the electrode potential on atomic-level properties in realistic device structures. The electrostatic potential is obtained from a finite element solution of Poisson's equation. The charge density is described at 4 levels of decreasing scale: the semiclassical approach, the effective mass approximation, the parameterized tight-binding method, and first principles density functional theory. The lattice dynamics is described with valence force fields for large systems and density function theory at finer levels. The coupling with the electromagnetic field is described with a density matrix approach or the Keldysh formalism. This talk will give an overview of the methods available at JPL and give a few illustrative examples, such as the modeling of spin qubits in Si/SiGe quantum dots, and transport properties in Si and SiGe nanowires.