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Adam Biacchi1 Son Le1 Brian Alberding1 Joseph Hagmann1 Curt Richter1 Edwin Heilweil1 Angela Hight Walker1

1, National Institute of Standards and Technology, Gaithersburg, Maryland, United States

Colloidal-based solution syntheses offer a scalable and cost-efficient means of producing nanoscale semiconductors in high yield. While much progress has been made towards the controlled and tailorable synthesis of semiconductor nanocrystals in solution, it remains a substantial challenge to fully characterize the products’ inherent carrier transport properties. This is often due to their irregular morphology or small dimensions, which usually demand the formation of colloidal assemblies or films as a prerequisite to performing electrical measurements. Here, we report a novel means for obtaining a comprehensive analyses of the electronic transport properties of individual colloidal semiconductor nanocrystals. First, we present the development of a novel solution chemistry-based synthetic approach to produce nearly monodisperse µm-scale 2D tin(II) sulfide (SnS) nanoribbons and square nanosheets using a one-pot, one-step, easily-scalable synthetic route. These syntheses represent a rare example in this size regime of essentially uniform, single-crystalline, 2D nanocrystals produced using colloidal chemistry. Next, we detail the structural characterization of these SnS materials, and describe how they are processed from solution to fabricate back-gated, top-contact solid-state devices from individual colloidal crystals. Finally, we interrogate their electronic transport properties by a combination of multi-point contact probe electrical transport measurements and time-resolved terahertz spectroscopy. These studies allow for the determination of carrier concentration, carrier mobility, conductivity, and the majority carrier type within an individual 2D colloidal nanocrystal. Our findings illustrate that minor manipulation of solution chemistries may afford products with substantively disparate charge carrier parameters, which are challenging to extract using common experimental practices, and underpins that this metrological strategy represents a significant and valuable advancement in the characterization of colloidally-synthesized semiconductors.

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