A project of the Theoretical Chemical and Quantum Physics Group


Mr. Jackson Smith, Mr. Jesse Vaitkus, Dr. Daniel Drumm, A/Prof. Jared Cole, and Prof. Salvy Russo

Brief Project Outline

We are rapidly approaching the lithography limit for manufacturing nanoelectronic devices. As these devices get smaller, their quantum properties become important. These properties can be used by quantum computers, which have the potential to revolutionise the field of computing and information processing.

To make components for a quantum computer, we must use bottom-up approaches to manufacturing. And, while we are not at a stage where large-scale commercial manufacturing is feasible, this technology has developed to the point where it is possible to have control over the manufacturing process with atomic precision. For example, new structures such as quantum dots, layers, and wires have all been made experimentally by doping silicon with phosphorus atoms at extremely high concentrations.

To understand how we can use these devices, we first need to understand their electronic structure. One of the strengths of our group is in performing highly accurate density-functional theory (DFT) calculations to find the ground-state electronic properties of nano-scale structures. The results of these DFT calculations are then used to build effective models for these devices using effective-mass theory, the nonequilibrium Green's functions formalism, and tight-binding theory. This many-pronged approach allows us to model systems that are of direct relavance to current experiments.

Illustration of a Si:P delta-doped layer

Illustration of a phosphorus (red atoms) in silicon (grey bonds) [Si:P] delta-doped layer. The ratio of phosphorus atoms to silicon atoms is equal to 1/4 inside the layer. These high doping densities and the strong spatial confinement of the phosphorus atoms leads to the interesting physical properties of these structure.

Isosurface of the donor electron wavefunction for a single P donor in Si

Isosurface (blue/red) of the donor electron wavefunction for a single phosphorus donor in silicon (yellow). By the doping of a single phosphorus atom into silicon, one electron is donated to the silicon lattice. Although this electron is bound to the phosphorus atom, the isosurface shows it is partially delocalised and spread throughout the silicon. The distance from the edge to the center of the picture is almost 3 nm. The fact the electron is spread out in space is a consequence of the wave-like nature of this fundamental particle.

Probability density of the donor electrons in a Si:P delta-doped wire

Probability density (black) of the donor electrons in an Si:P delta-doped wire. This picture gives us an idea of the shape of the wire and the space within which a current will flow through the device.

Recent Publications

J. S. Smith, J. H. Cole and S. P. Russo, Electronic properties of d-doped Si:P and Ge:P layers in the high-density limit using a Thomas-Fermi method, Phys. Rev. B 89 035306 (2014)

D. W. Drumm, J. S. Smith, M. C. Per, A. Budi, L. C. L. Hollenberg, and S. P. Russo, Ab initio Electronic Properties of Monolayer Phosphorus Nanowires, Phys. Rev. Lett. 110 126802 (2013)

For more information about this project, please contact Jared Cole or Salvy Russo.