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Red spectral shift and enhanced quantum efficiency in phonon-free photoluminescence from silicon nanocrystals

Nature Nanotechnology volume 5, pages 878–884 (2010)Cite this article

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Abstract

Crystalline silicon is the most important semiconductor material in the electronics industry. However, silicon has poor optical properties because of its indirect bandgap, which prevents the efficient emission and absorption of light. The energy structure of silicon can be manipulated through quantum confinement effects, and the excitonic emission from silicon nanocrystals increases in intensity and shifts to shorter wavelengths (a blueshift) as the size of the nanocrystals is reduced. Here we report experimental evidence for a short-lived visible band in the photoluminescence spectrum of silicon nanocrystals that increases in intensity and shifts to longer wavelengths (a redshift) with smaller nanocrystal sizes. This higher intensity indicates an increased quantum efficiency, which for 2.5-nm-diameter nanocrystals is enhanced by three orders of magnitude compared to bulk silicon. We assign this band to the radiative recombination of non-equilibrium electron–hole pairs in a process that does not involve phonons.

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Figure 1: Temporal and spectral characteristics of PL for nanocrystals with an average diameter of 4.5 nm.
Figure 2: Hot PL and excitonic PL bands for all samples.
Figure 3: Carrier relaxation paths for low (Nexc < 1) and high (Nexc > 1) excitation flux.
Figure 4: Comparison of time-resolved spectral dependence of PL intensity for a sample with an average diameter of 2.5 nm under pulsed (Δt = 2 ps) and semi-c.w. (Δt = 5 ns) excitation at λexc = 325 nm.
Figure 5: Comparison of relative intensity of hot and excitonic PL bands for nanocrystals with an average diameter of 2.5 nm and 4 nm.

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Acknowledgements

The authors thank M. Fujii (Kobe University) for sharing expertise on the preparation of sputtered layers, A.N. Poddubny, A.A. Prokofiev and A.S. Moskalenko (A.F. Ioffe Physico-Technical Institute) for discussions and theoretical insights, D. Bebelaar (University of Amsterdam) for technical assistance, and K. van der Vaart for contributing to the initial phase of the experiments. This work was financially supported by Stichting voor de Technologische Wetenschappen (STW), Stichting der Fundamenteel Onderzoek der Materie (FOM), and Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO).

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Authors and Affiliations

  1. Van der Waals—Zeeman Institute, University of Amsterdam, Kruislaan 904, XH Amsterdam, NL-1098, The Netherlands

    W. D. A. M. de Boer, D. Timmerman, K. Dohnalová & T. Gregorkiewicz

  2. Ioffe Physico-Technical Institute of RAS, 26 Polytechnicheskaya, St Petersburg, 194021, Russia

    I. N. Yassievich

  3. Van't Hoff Institute for Molecular Sciences, University of Amsterdam, Nieuwe Achtergracht 129, WS Amsterdam, NL-1018, The Netherlands

    H. Zhang & W. J. Buma

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  1. W. D. A. M. de Boer
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Contributions

W.d.B. and T.G. conceived the project, designed the experiments and co-wrote the manuscript. W.d.B. performed experiments and data analysis. D.T. prepared the Si-NC layers. I.N.Y. provided theoretical interpretations and modelling. K.D. contributed essentially to finalization of the manuscript. H.Z. and W.J.B. facilitated picosecond PL spectroscopy and provided the necessary expertise. T.G. supervised and facilitated the project. All authors discussed the results and commented on the manuscript.

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Correspondence to W. D. A. M. de Boer.

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de Boer, W., Timmerman, D., Dohnalová, K. et al. Red spectral shift and enhanced quantum efficiency in phonon-free photoluminescence from silicon nanocrystals. Nature Nanotech 5, 878–884 (2010). https://doi.org/10.1038/nnano.2010.236

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