Martin Gnauck

Publications (2)26.4 Total impact

• Article: Direct determination of minority carrier diffusion lengths at axial GaAs nanowire p-n junctions.

  Christoph Gutsche, Raphael Niepelt, Martin Gnauck, Andrey Lysov, Werner Prost, Carsten Ronning, Franz-Josef Tegude
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  ABSTRACT: Axial GaAs nanowire p-n diodes, possibly one of the core elements of future nanowire solar cells and light emitters, were grown via the Au-assisted vapor-liquid-solid mode, contacted by electron beam lithography, and investigated using electron beam induced current measurements. The minority carrier diffusion lengths and dynamics of both, electrons and holes, were determined directly at the vicinity of the p-n junction. The generated photocurrent shows an exponential decay on both sides of the junction and the extracted diffusion lengths are about 1 order of magnitude lower compared to bulk material due to surface recombination. Moreover, the observed strong diameter-dependence is well in line with the surface-to-volume ratio of semiconductor nanowires. Estimating the surface recombination velocities clearly indicates a nonabrupt p-n junction, which is in essential agreement with the model of delayed dopant incorporation in the Au-assisted vapor-liquid-solid mechanism. Surface passivation using ammonium sulfide effectively reduces the surface recombination and thus leads to higher minority carrier diffusion lengths.
  Nano Letters 02/2012; 12(3):1453-8. · 13.20 Impact Factor
• Article: Strongly enhanced molecular fluorescence inside a nanoscale waveguide gap.

  Volker J Sorger, Nitipat Pholchai, Ertugrul Cubukcu, Rupert F Oulton, Pavel Kolchin, Christian Borschel, Martin Gnauck, Carsten Ronning, Xiang Zhang
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  ABSTRACT: We experimentally demonstrate dramatically enhanced light-matter interaction for molecules placed inside the nanometer scale gap of a plasmonic waveguide. We observe spontaneous emission rate enhancements of up to about 60 times due to strong optical localization in two dimensions. This rate enhancement is a nonresonant nature of the plasmonic waveguide under study overcoming the fundamental bandwidth limitation of conventional devices. Moreover, we show that about 85% of molecular emission couples into the waveguide highlighting the dominance of the nanoscale optical mode in competing with quenching processes. Such optics at molecular length scales paves the way toward integrated on-chip photon source, rapid transfer of quantum information, and efficient light extraction for solid-state-lighting devices.
  Nano Letters 11/2011; 11(11):4907-11. · 13.20 Impact Factor