PhD Opportunities for 2013!
ELECTRONIC PROPERTIES OF SILICON NANODEVICES
The project aims to uncover and harness new electronic
properties of silicon nanodevices in which quantum mechanical effects
play crucial roles.
If you place two current carrying wires close together in
parallel one might expect that not a lot happens, except that the wires
experience forces due to the resulting magnetic fields. The microscopic
origin of electrical current is, however, the motion of charge
carriers: electrons in this case. Electrons in each of the wires feel
the net effect of the motion of electrons in the other wire through the
net magnetic field. Effects due to the individual nature of electrons
So what happens if you bring the wires so close together that
electrons in one
This project aims to produce experimental answers to these
questions for charge carriers generated in nanostructures built using
state-of –the-art silicon technology. It forms part of an ongoing
project to explore new physical regimes using silicon technology, at
the same time providing useful physical insights into these
technologically vital silicon-based structures.
2/3. SILICON VALLEYTRONICS
The interface between silicon and silicon dioxide is the basis on which much of modern information and communication technology is built. It is also the substrate or host material of choice for a wide range of scientific and technological investigations. Owing to its ubiquity, long history and importance in society, its basic properties are often assumed to be well understood. Recent experiments, however, have unexpectedly revealed that certain preparation conditions lead to a new type of interface at which the electronic properties are profoundly altered. These experiments show that an aspect of silicon band-structure known as “valley-splitting” can be enlarged well beyond an order of magnitude than had previously been possible, and that its magnitude can be tuned flexibly, in-situ, using standard electrical gates [PRL 96, 236801 (2006)]. The band-structure of a material lies at the very heart of the physics of any crystalline solid dictating all properties involving electrons such as how suitable the material is for use in a transistor and what colour of light the material absorbs and emits. As such, large alterations to valley-splitting can be expected to have far reaching consequences for a variety of physical properties. At present, however, we know little about this effect – what causes it and what consequences it has; the new interface is a new material with unknown properties.
This project aims to experimentally establish what causes this newly discovered giant valleysplitting effect and the consequences this has on electrical and optical properties. Since the valley-splitting is electrically tuneable, new properties discovered at large valley-splitting will also be electrically tuneable or switchable. Furthermore, this silicon–silicon dioxide material system is automatically compatible with the vast arsenal of cutting-edge silicon technology. Any new functionality can be embedded into silicon-based systems at the very deepest level of integration.
3/3. NEW SILICON-BASED NANOSTRUCTURES BY DIRECT BONDING
The vast range of applications semiconductor structures have found partly stems from our ability to tailor their physical properties. This is often achieved by creating a stack of thin layers of mono-crystalline semiconductors which enables the electronic band-structure to be engineered. These “heterostructures” are usually made by hetero-epitaxial techniques such as MBE (Molecular Beam Epitaxy) or MOVPE (Metal-Organic Vapour Phase Epitaxy). These techniques, however, are fundamentally limited as to the material combinations that can be embedded in a structure. This in turn limits what we can get the semiconductor structures to do.
However, there is an alternative method of making
heterostructures, which is to use recently developed techniques of
direct bonding and layer transfer. Direct bonding is a method of
sticking two materials together in which two sufficiently flat and
clean surfaces are initially held together by van der Waals forces and
hydrogen bonds and then, thermally treated allowing the materials to
fuse. In layer transfer, a layer of material prepared on a sacrificial
substrate can be transferred onto another wafer by direct bonding,
followed by the removal of
The project will aim to create new structures that were impossible by hetero-epitaxial techniques by using direct bonding and layer transfer and to assess their physical properties. The goal is to create new devices with new functionalities, and new structures enabling new physical regimes to be accessed for fundamental physics experiments.
NANODEVICES FROM BIOLOGICAL LIQUID CRYSTALS
Applicants should have a background in the physical sciences
or expect to gain a First or Upper Second Class UK Honours degree, or
the equivalent from an overseas University. Possible funding sources
include the Doctoral Training Account (for UK applicants) or
Faculty/University studentships and scholarships. Applications from
self-funded students are always welcome.
Please contact me by sending me an e-mail in the first instance.