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      SCANNING PHOTOCURRENT MICROSCOPY IN SEMICONDUCTOR NANOSTRUCTURES

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      Modern Physics Letters B
      World Scientific Pub Co Pte Lt

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          Characteristics of the Surface-State Charge (Qss) of Thermally Oxidized Silicon

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            Imaging of photocurrent generation and collection in single-layer graphene.

            Unlike in linear nanostructures, photocurrent generated in single-layer graphene (SLG) is expected to display two-dimensional characteristics. This allows the investigation of carrier dynamics, in relation to several spatially varying factors (such as the location of photocurrent generation and collection) and the overall electron band configuration of the SLG. In this letter, we use scanning photocurrent microscopy to investigate the spatial mapping of photocurrent generation and collection in SLG in a multielectrode geometry. A strong electric field near metal-graphene contacts leads to efficient photocurrent generation, resulting in >30% efficiency for electron-hole separation. The polarity and magnitude of contact photocurrent are used to study the band alignment and graphene electrical potential near contacts, from which it is shown that there exist large-scale spatial variations in graphene electric potential. Our measurements with a multielectrode device configuration reveal that photocurrent is distributed with a clear directional dependence among different collector electrodes. In the same measurement scheme, we also determine the majority carrier in graphene under different gate conditions by imaging the thermocurrent generated by laser-induced heating of electrodes.
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              Large and tunable photo-thermoelectric effect in single-layer MoS2

              We study the photoresponse of single-layer MoS2 field-effect transistors by scanning photocurrent microscopy. We find that, unlike in many other semiconductors, the photocurrent generation in single-layer MoS2 is dominated by the photo-thermoelectric effect and not by the separation of photoexcited electron-hole pairs across the Schottky barriers at the MoS2/electrode interfaces. We observe a large value for the Seebeck coefficient for single-layer MoS2 that, by an external electric field, can be tuned between -4x10^2 uV/K and -1x10^5 uV/K. This large and tunable Seebeck coefficient of the single-layer MoS2 paves the way to new applications of this material such as on-chip thermopower generation and waste thermal energy harvesting.
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                Author and article information

                Journal
                Modern Physics Letters B
                Mod. Phys. Lett. B
                World Scientific Pub Co Pte Lt
                0217-9849
                1793-6640
                October 10 2013
                October 10 2013
                : 27
                : 25
                : 1330018
                Article
                10.1142/S0217984913300184
                270dfe3a-7bd9-4ad6-b7de-809b0bc7a9bc
                © 2013
                History

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