Saturday, September 6, 2008


Surface-related states in oxidized silicon nanocrystals enhance carrier relaxation and inhibit Auger recombination
Andreas Othonos^1* , Emmanouil Lioudakis^1  A. G. Nassiopoulou^2 
^1 Department of Physics, Research Center of Ultrafast Science, University of Cyprus P.O. Box 20537, 1678, Nicosia, Cyprus
^2 IMEL/NCSR Demokritos, Terma Patriarchou Grigoriou, Aghia Paraskevi, 153 10 Athens, Greece 

Silicon is considered as the key material of today’s integrated circuit technology; however, one of the major drawbacks of this semiconductor is its inability to efficiently emit light. The observation of efficient photoluminescence a few years ago from porous silicon [1-4] and silicon nanocrystals [5] has provided hope for Si-based optoelectronics and has stirred research interest in the area of Si nanostructures as a potential candidate for silicon based emission devices [6-9]. It is well known that semiconductor nanocrystals (NCs) exhibit interesting size dependent properties, mainly due to the large fraction of surface atoms to the total number of atoms in the NC and quantum size effects that may allow tuning of the light emission peak from such nanostructures. Although there have been different forms of Si nanocrystals manufactured, Si-NCs embedded in a amorphous SiO2 matrix [10, 11] have gained considerable interest due to their PL stability with time for light emission applications and their nanoelectronics applications. Since the demonstration of this type of Si-NCs there has been a significant research interest in their photoluminescence properties, with little emphasis on the ultrafast carrier dynamics [12].

In this work we have studied femtosecond carrier dynamics in oxidized silicon NCs and the role that surface-related states play to the various relaxation mechanisms over a broad range of photon excitation energy corresponding to energy levels below and above the direct bandgap of the formed NCs [13]. Transient photoinduced absorption techniques [14] have been employed to investigate the effects of surface-related states on the relaxation dynamics of photogenerated carriers in 2.8 nm oxidized silicon NCs. Independent of the excitation photon energy, non-degenerate measurements reveal several distinct relaxation regions corresponding to relaxation of photoexcited carriers from the initial excited states, the lowest indirect states and the surface-related states. Furthermore, degenerate and non-degenerate measurements at difference excitation fluences reveal a linear dependence of the maximum of the photoinduced absorption signal and an identical decay suggesting that Auger recombination does not play a significant role in these nanostructures even for fluence generating up to 20 carriers/NC.

Video Content Length 20:00 Copyright: © 2008 Othonos et al

[1] L. Canham, Appl. Phys. Lett. 57, 1046 (1990).
[2] H. Koyama and N. Koshida,  Journal of Applied Physics, 74, 6365 (1993).
[3]  H. Mizuto, H. Koyama, and N. Koshida, Appl. Phys. Lett., 69, 3779 (1996).
[4]  A. G. Cullis, L. T. Canham and P. D. J. Calcott  J. Appl. Phys. 82, 909 (1997).
[5]  T. Shimizu-Iwayama, M. Ohshima, T. Niimi, S. Nakao, K. Saitoh, T. Fujita, and N. Itoh, J. Phys.: Condens. Matter 5, L375 (1993).
[6]  F. Iacona, D. Pacifici, A. Irrera, M. Miritello, G. Franzo, F. Priolo, D. Sanfilippo, G. Di Stefano and P.G. Fallica, Appl. Phys. Lett. 81 3242 (2002).
[7]  Y. Kanemitsu, T. Ogawa, K. Shiraishi, and K. Takeda, Phys. Rev. B 48, 4883 (1993).
[8]  K. S. Min, K. V. Shcheglov, C. M. Yang, H. A. Atwater, M. L. Brongersma, and A. Polman, Appl. Phys. Lett. 69, 2033 (1996).
[9]  J. Linnros, N. Lalic, A. Galeckas, and V. Grivickas, J. Appl. Phys. 86, 6128 (1999).
[10] A. G. Nassiopoulou, Encyclopedia of Nanoscience and Nanotechnology, edited by H. S. Nalwa (American Scientific Publishers, California, 2004), vol. 9 p. 793-813, (2004).
[11] J  Heitmann, F. Muller, M. Zacharias and U Gosele, Advanced Materials 17 (7) 795 (2005).
[12] E. Lioudakis, A.G. Nassiopoulou, A. Othonos, Appl. Phys. Lett. 90, 171103 (2007).
[13] A. Othonos, E. Lioudakis, A.G. Nassiopoulou, accepted for publication in Nanoscale Research Letters.
[14] A. Othonos,  J. Appl. Phys. 83, 1789 (1998).
A. Othonos, E. Lioudakis, and A. G. Nassiopoulou,
OAtube Nanotechnology 1, 903 (2008).
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