Terahertz Spectroscopy of Semiconductor Nanowires

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Nanostructures such as carbon nanotubes and ZnO nano-particles are already being used in commercialproducts such as tyres and sunscreens. However, despite progress in understanding the mechanical andoptical properties of nano-materials we are still at the dawn of the fields of nano-optoelectronics andnano-photonics. Advances in understanding the fundamental materials science of these nano-materials todaywill therefore have a major impact on a wide range of commercial products over the next 30 years. One of thedifficulties with developing nano-optoelectronic components is the complexity of measuring their electricalproperties. Traditionally, new materials and devices have been tested via electrical transport measurements.Unfortunately, it is extremely difficult to make electrical contacts on a 30nm diameter nano-wire or anano-particle. Indeed even if the contacts are made it is then difficult to separate the properties of thenano-material from those of the contact. Additionally, such measurements are plagued by reproducibilityproblems. Thus there is a pressing need for techniques that can quickly and reliably extract the electricalproperties of nano-structured materials. The availability of such techniques would greatly accelerate thedevelopment of new materials and allow devices based on these materials to be brought to the market sooner.We propose to solve these problems by applying the technique of optical pump terahertz probe spectroscopy(OPTPS) to semiconductor nano-wires, and by developing refined models to extract the most importantdevice-specific electrical properties from the measured data. The knowledge we gain will help us develop newoptoelectronic devices based on semiconductor nano-wires.