The Computational Condensed Matter and Nanoelectronics (CCMN) research group of the University of Chester aims to carry out state-of-the-art ab initio computational modelling that discerns the underlying quantum mechanical nature of organic and crystalline materials as well as heterostructures, from the point of view of fundamental physics and technological applications in nanoelectronics and optoelectronics.
The field of Nanoelectronics is concerned with materials, devices, circuits and systems relevant to contemporary integrated circuits (ICs). Modern ICs which are the ‘electronic brain’ and memory, inside mobile phones, laptop and desktop PCs are comprised of billions of Field Effect Transistors (FETs). The gate length of such an FET, ~10 nm, constitutes an in service nanodevice. The gate is the terminal that controls the current flow through the channel from the source to the drain, thus the FET acts as a switch. At this length scale, where an FET consists of few hundred atoms, quantum mechanics must be applied to decipher its operating principles, and the engineer must draw upon the expertise from Condensed Matter Physics.
At CCMN, we investigate numerically the electron flow in exotic topological insulator materials, which can be incorporated in the channel of an FET. We also examine, via computer simulation, the revolutionary Quantum Dot Cellular Automata (QCA) devices and circuits, a brand-new paradigm for computer architecture. QCA are transistorless and the charge configuration of quantum dots encodes binary information. In particular, we perform numerical calculations for the switching of QCA mixed valence molecule and simulate the Clocking of Molecular QCA, by lithographically defined wires, buried in the substrate, with the molecules located at the surface.
We are also engaged in fundamental computational research exploring the electron-electron interaction, in the homogeneous electron gas (HEG), employing the quantum Monte Carlo technique. The HEG consists of a sea of electrons together with a uniform positive background charge density. Information gleaned from numerical studies of the HEG form the basis of the exchange-correlation functionals, used in almost all density functional theory simulations of real materials. We also investigate the Coulomb attraction between electrons and holes in layered semiconductor systems. Our calculations show that at low electron densities isolated few-body species are present, while at higher electron densities collective, many-body behaviour is observed.
Computational modelling from first-principles is also employed to investigate the electronic structure of materials surfaces and interfaces in the presence of defects and impurities. In electronic and optoelectronic devices, such as solar cells and light emitting diodes, it is crucial to optimise the energy level alignment between materials interfaces, in order to improve device efficiency. We work in close contact with experimental groups that are experts in device fabrication and use our computational methodology complementary to acquire deeper understanding of the interplay between quantum mechanics, solid state physics, surface and interface science and device physics. We also conduct research in charge and exciton transport in organic thin films using a combination of first-principles modelling and kinetic Monte Carlo, relevant to optoelectronic applications such as organic solar cells. Finally, using a combination of density functional theory and the Landauer-Buttiker formalism, we are able to extract electron transport properties of molecular wires, which may form the interconnects for future molecular electronic devices.
