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F1.09 - Ultrafast Electrical Properties of Photoexcited Silicon Nanostructures 
April 22, 2014   11:30am - 11:45am

Semiconductor nanostructures are increasingly being explored as key components for novel optoelectronic devices like photovoltaics. Though a strong effort has been made to understand their optical properties, such as absorption and photoluminescence, it still remains difficult to quantify the electrical properties of these small structures, especially at ultrafast time scales. Here we present results on the mobilities and carrier dynamics of silicon nanowires and silicon nanocrystals by utilizing a contactless electrical probe that has sub-picosecond time resolution. This technique relies on the absorption of THz radiation by free carriers in the nanostructures produced by an ultrafast laser pulse. We will present our observations of a drastic change in the free carrier dynamics as the Si geometry is decreased. The mobilities for the different Si structures for varying absorbed pump fluences were also studied. As the volume of Si is reduced, the mobility decreases, which we will show is due to the enhanced carrier-carrier and surface interactions. These experiments demonstrate the benefit of using a nanowire geometry as they can effectively, and directionally, transport charge. For SiNCs, however, charge transport would need to be enhanced through improved electrical coupling between dots, or transport to another conductive material, in order to effectively move carriers in a photovoltaic device.

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Keynote Address
Panel Discussion - Different Approaches to Commercializing Materials Research
Business Challenges to Starting a Materials-Based Company
Fred Kavli Distinguished Lectureship in Nanoscience
Application of In-situ X-ray Absorption, Emission and Powder Diffraction Studies in Nanomaterials Research - From the Design of an In-situ Experiment to Data Analysis