Welcome to the Colton group research homepage! The main research focus in our lab is the optical investigation of semiconductors and various semiconductor nanostructures. Some of the properties we measure are spin lifetimes, photoluminescence, and band gap energies. Electron spin lifetimes have particularly interesting applications to the field of quantum computing (see explanation below). For more information about our research, see the links to the left. Specifically, our research page describes several of the experiments we're currently working on. The basics of semiconductors page contains a brief introduction to the physics behind our experiments, and the optical experiments page describes some of the different techniques we use.
Colton research group, May 2018
Optical Investigations of Nanostructures
Most of our recent publications have involved measuring spin properties of electrons. Spin states of electrons in semiconductors have been the focus of much recent research due to the twin emerging fields of spintronics and spin-based quantum computing. Spintronics involves actively using the spin of an electron together with its charge in the operation of nanoscale electronic devices. Interesting applications of spintronics include giant magneto-resistance (GMR), the discovery of which was awarded the 2007 Nobel Prize in Physics and which now is used extensively in hard disk read heads; magnetic random access memory (MRAM) a non-volatile memory now being used in applications such as computers in satellites; and spin-LEDs, which are light-emitting diodes that produce circularly polarized light by orienting the spin of the electrons inside the diode structure.
Spin-based quantum computing involves using quantum mechanical spin states as the "1"s and "0"s of a computer for storage and calculation. Quantum computers will use these states and quantum mechanical operations to solve certain kinds of problems exponentially faster than classical computers. Examples of such problems include database searching and the cryptographic task of factoring large numbers into primes. Using the spin states of electrons in semiconductor nanostructures for the quantum-mechanical bits (qubits) of such a computer was first proposed in 1998, and has been the subject of much theoretical and experimental research ever since.
For electrons to be used in qubits and spintronic devices, their spin states must be controllable. Undesired interaction with environmental factors such as nuclear spins and phonons can lead to decoherence. To prevent unwanted changes to qubits, this decoherence must be small enough that it does not irreversibly affect the quantum state of the computer on the time scale of the computing operations. In order for spin-based nanosystems to function, they must therefore be implemented in materials which have relatively long spin lifetimes. Finding out which materials have the best spin dynamic properties will help characterize materials for spintronic and quantum computing applications.
Our lab is currently investigating nanoparticle synthesis using the protein ferritin. Ferritin is a spherical protein that is especially useful for nanoparticle formation, because it offers a uniformly-sized shell in which to synthesize the nanoparticles. By varying the combinations of metals inside the ferritin shell, it is possible to create nanoparticles which have a variety of band gaps.
One of the primary applications for these nanoparticles is in multi-junction solar cells. Traditional single-junction solar cells have a maximum theoretical efficiency of only 33.7%; however, by using multiple layers of material, the maximum efficiency can be increased to over 80%. These layers need to have the proper band gaps in order to absorb the maximum amount of light, and we are searching for the proper combination of nanoparticles to use for a high-efficiency solar cell of this type.