si nano - Hindawi Publishing Corporation Advances in...

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Hindawi Publishing Corporation Advances in Optical Technologies Volume 2008, Article ID 279502, 32 pages doi:10.1155/2008/279502 Review Article Silicon Nanocrystals: Fundamental Theory and Implications for Stimulated Emission V. A . B e l y a kov , 1 V. A . B u r d ov , 1 R. Lockwood, 2 and A. Meldrum 2 1 Department of Theoretical Physics, University of Nizhniy Novgorod, pr. Gagarina 23, Nizhniy Novgorod 603950, Russia 2 Department of Physics, University of Alberta, Edmonton, AB, Canada T6G2G7 Correspondence should be addressed to A. Meldrum, ameldrum@ualberta.ca Received 18 February 2008; Accepted 9 May 2008 Recommended by D. Lockwood Silicon nanocrystals (NCs) represent one of the most promising material systems for light emission applications in microphotonics. In recent years, several groups have reported on the observation of optical gain or stimulated emission in silicon NCs or in porous silicon (PSi). These results suggest that silicon-NC-based waveguide ampli±ers or silicon lasers are achievable. However, in order to obtain clear and reproducible evidence of stimulated emission, it is necessary to understand the physical mechanisms at work in the light emission process. In this paper, we report on the detailed theoretical aspects of the energy levels and recombination rates in doped and undoped Si NCs, and we discuss the e f ects of energy transfer mechanisms. The theoretical calculations are extended toward computational simulations of ensembles of interacting nanocrystals. We will show that inhomogeneous broadening and energy transfer remain signi±cant problems that must be overcome in order to improve the gain pro±le and to minimize nonradiative e f ects. Finally, we suggest means by which these objectives may be achieved. Copyright © 2008 V. A. Belyakov et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1. INTRODUCTION Silicon is the most widespread semiconductor in modern microelectronics technologies. Its natural abundance, low cost, and high purity, as well as the high electronic quality of the Si/SiO 2 interface, have led to its overwhelming dominance in microelectronic devices. Nevertheless, the use of silicon in optoelectronics remains highly limited. This state of a f airs has remained, in fact, almost unchanged because of a fundamental property of the silicon band structure—the indirect band gap. The indirect radiative interband transitions in bulk Si are strongly suppressed because an emitted photon cannot satisfy the momentum conservation law for transitions from the conduction-band minimum ( Δ -point) to the top of the valence band ( Γ -point). The photon wave vector is about three orders of magnitude less than that required for the transition between the Δ -and Γ -points. This di f erence in k - space is k Δ = 0 . 86 × 2 π/a 0 ,with a 0 being the lattice constant of silicon, equal to 5.43 ˚ A. The electron-hole radiative
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si nano - Hindawi Publishing Corporation Advances in...

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