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Direct generation of multiple excitons in adjacent silicon nanocrystals revealed by induced absorption

Nature Photonics volume 6, pages 316–321 (2012)Cite this article

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Abstract

The enhancement of carrier multiplication in semiconductor nanocrystals attracts a great deal of attention because of its potential in photovoltaic applications. Here, we present the results of investigations of a novel carrier multiplication mechanism recently proposed for closely spaced silicon nanocrystals in SiO2 on the basis of photoluminescence. Using ultrafast pump–probe spectroscopy rigorously calibrated for the number of absorbed photons, we find that adjacent nanocrystals are excited directly upon absorption of a single high-energy photon. We demonstrate efficient carrier multiplication with an onset close to the energy conservation threshold of twice the bandgap, 2Eg. Moreover, with absorption of a single high-energy photon under low pump fluence conditions, it was found that carrier–carrier interaction was significantly suppressed, but the amplitude of the signal was enhanced. We show that these results are in excellent agreement with the dependence of photoluminescence quantum yield on excitation, as reported previously for similar materials.

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Figure 1: Induced absorption signal for different excitation photon energies.
Figure 2: Possible microscopic mechanisms for spatially separated carrier multiplication.
Figure 3: Evidence for the direct mechanism of spatially separated carrier multiplication.

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Acknowledgements

The authors thank M. Fujii (Kobe University) for sharing expertise on the preparation of sputtered layers, and K. Dohnalová and D. Timmerman for discussions and comments. This work was financially sponsored by Stichting voor de Technische Wetenschappen (STW) and NanoNextNL.

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Authors and Affiliations

  1. Van der Waals-Zeeman Institute, University of Amsterdam, Science Park 904, Amsterdam, 1098 XH, The Netherlands

    M. Tuan Trinh, Rens Limpens, Wieteke D. A. M. de Boer & Tom Gregorkiewicz

  2. Department of Chemical Engineering, Optoelectronic Materials Section, Delft University of Technology, Julianalaan 136, Delft, 2628 BL, The Netherlands

    Juleon M. Schins & Laurens D. A. Siebbeles

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  1. M. Tuan Trinh
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Contributions

M.T.T. and T.G. conceived the project. M.T.T. designed and performed the experiments and data analysis, and wrote the manuscript. J.M.S. and L.D.A.S. facilitated femtosecond absorption experiments. R.L. and W.dB. contributed to the experimental part and the concept of the project, respectively. T.G. supervised the project. All authors discussed the results and commented on the manuscript.

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Correspondence to M. Tuan Trinh or Tom Gregorkiewicz.

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Trinh, M., Limpens, R., de Boer, W. et al. Direct generation of multiple excitons in adjacent silicon nanocrystals revealed by induced absorption. Nature Photon 6, 316–321 (2012). https://doi.org/10.1038/nphoton.2012.36

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