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Size, Shape, and Crystallinity of Luminescent Structures in Oxidized Si Nanoclusters and H-Passivated Porous Si

  • S. Schuppler (a1), S. L. Friedman (a1), M. A. Marcus (a1), D.L. Adler (a1), Y.-H. Xie (a1), F. M. Ross (a2), T. D. Harris (a1), W.L. Brown (a1), Y. J. Chabal (a1), P. J. Szajowski (a1), E. E. Chaban (a1), L. E. Brus (a1) and P. H. Citrin (a1)...

Abstract

Near-edge and extended x-ray absorption fine structure measurements from a wide variety of H-passivated porous Si samples and oxidized Si nanocrystals, combined with electron microscopy, ir-absorption, α-recoil, and luminescence emission data, provide a consistent structural picture of the species responsible for the luminescence observed in these systems. For luminescent porous Si samples peaking in the visible region, i. e., ≤700nm, their mass-weighted-average structures are determined here to be particles–not wires, whose short-range character is crystalline – not amorphous, and whose dimensions – typically <15 Å – are significantly smaller than previously reported or proposed. These results depend only on sample luminescence behavior, not on sample preparation details, and thus have general implications in describing the mechanism responsible for visible luminescence in porous silicon. New results are also presented which demonstrate that the observed luminescence is unrelated to either the photo-oxidized Si species in porous Si or the interfacial suboxide species in the Si nanocrystals.

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References

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1 For example, see (a) Mater. Res. Soc. Proc. 256 (1992); (b) ibid. 283 (1993); (c) ibid. 298 (1993).
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3 Lehmann, V. and Gösele, U., Appl. Phys. Lett. 58, 856 (1991).
4 Schuppler, S., Friedman, S. L., Marcus, M. A., Adler, D. L., Xie, Y.-H., Ross, F. M., Harris, T. D., Brown, W. L., Chabal, Y. J., Brus, L. E., and Citrin, P. H., Phys. Rev. Lett. 72, 2648 (1994).
5 MacDowell, A. A., Hashizume, T., and Citrin, P. H., Rev. Sci. Instr. 60, 1901 (1989).
6 Preparations of the por-Si samples studied here (referred to as A, B, C, and D) follow those in Refs. 2, 7, and 8, namely, C [2]: p-type Si(100), >50 Ω-cm, 20%HF in alcohol, 20 mA/cm2 for 5 min; A [8]; same as C, but etched 60 min; B [7]: p-type Si(100), >50 Ω-cm, 15%HF in alcohol, 25 mA/cm2 for 12 min; D[8]: p-type Si(100), 0.5-0.8 Ω-cm, 40% HF in alcohol, 50 mA/cm2 for 80 sec, soaked 2 hr unetched in same solution.
7 Friedman, S. L., Marcus, M. A., Adler, D. L., Xie, Y.-H., Harris, T. D., and Citrin, P. H., Appl. Phys. Lett. 62, 1934 (1993).
8 Xie, Y. H., Hybertsen, M. S., Wilson, W. L., Ipri, S. A., Carver, G. E., Brown, W. L., Dons, E., Weir, B. E., R.Kortan, A., Watson, G. P., and Liddle, A. J., Phys. Rev. B 49, 5386 (1994); Y.-H. Xie (unpublished).
9 Oxidized Si nanocrystals were made by homogeneous nucleation in high-pressure He at 1000°C from thermal decomposition of disilane with subsequent oxidation in 02 at 1000°C for -30 msec. See Littau, K. A., Szajowski, P. J., Muller, A. J., Kortan, A. R., and Brus, L. E., J. Phys. Chem. 97, 122 (1993); W. L. Wilson, P. J. Szajowski, and L. E. Brus, Science 262,1242 (1993); P. J. Szajowski and L. E. Brus (unpublished).
10 Brus, L. E., Szajowski, P. F., Wilson, W. L., Harris, T. D., Schuppler, S., and Citrin, P. H., J. Amer. Chem. Soc. (to be published).
11 This por-Si sample more closely approximates the Si core because it contains less long- range order than c-Si. The results are completely unaffected by this choice because only difference spectra are being compared.
12 Lee, P. A., Citrin, P. H., Eisenberger, P., and Kincaid, B. M., Rev. Mod. Phys. 53, 769 (1981).
13 Street, R. A., Hydrogenated Amorphous Silicon (Cambridge University Press, Cambridge, 1991).
14 Cohen, B. L., Fink, C. L., and Degnan, J. H., J. Appl. Phys. 43, 19 (1972).
15 The volumes used for integrating the measured SiHx concentrations in the por-Si samples were obtained from TEM.
16 Surface sensitivity of <1um was obtained using a grazing internal incidence angle in a Ge plate positioned next to the por-Si samples.
17 For a Si cube of side L, NSi = 8L3/a0 3 for a sphere of diameter L, NSi sph = (π/6)NSi cube.
18 See, e. g., Delerue, C., Allan, G., and Lannoo, M., Phys. Rev. B 48, 11024 (1993), and references therein.

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