Exciton characteristics and exciton luminescence of silicon quantum dot structures
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IMENSIONAL SYSTEMS
Exciton Characteristics and Exciton Luminescence of Silicon Quantum Dot Structures I. M. Kupchak*, D. V. Korbutyak*, Yu. V. Kryuchenko*^, A. V. Sachenko*, I. O. Sokolovskiœ*, and O. M. Sreseli** *Lashkarev Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Kiev, 03028 Ukraine ^e-mail: [email protected] **Ioffe Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia Submitted May 31, 2005; accepted for publication June 15, 2005
Abstract—The exciton binding energy, the energies of the basic radiative exciton transition, and the zerophonon radiative lifetime of excitons in silicon quantum dots embedded in the SiOx matrix are calculated in effective mass approximation with quadratic dispersion relation. In addition, the spectra of steady-state photoluminescence and of time-resolved photoluminescence of excitons in the silicon quantum dots are calculated, and the kinetics of the photoluminescence relaxation is considered. The theory is compared with the experiment. It is shown that, for nanostructures involving silicon quantum dots with diameters smaller than 4 nm, the governing factor in the broadening of the spectral photoluminescence bands is the effect of mesoscopic quantum fluctuations. In this case, either an even one dangling bond at the interface, or one intrinsic point defect, or one foreign atom located inside the small-sized nanocrystallite or in its close surroundings produces a pronounced effect on the energy of the exciton transition. PACS numbers: 71.35.Gg, 78.55.-m, 78.67.Hc DOI: 10.1134/S1063782606010179
1. INTRODUCTION
effects can be rather profound, since a considerable (or even major) part of the force lines of the Coulomb interaction between the charges in a QD can be closed just through the environment. Specifically, the screening of the interaction between the charges by the barrier regions can have a noticeable effect on the electron– hole states in the QD. The second group of models is based on the envelope wave function method and characteristics of the band spectrum; i.e., on the solid-state approach for describing nanocrystallites. Clearly, these models are more adequate for describing the relatively large-sized QDs, in which the crystal structure starts to play an important role. In practice, this occurs even at the crystallite sizes ≥2 nm, although the calculations in the context of these models are often extended formally to smaller-sized QDs. In such approaches it is, to some extent, possible to account for the effect of barrier surroundings, and the polarization of the heterointerface by charge carriers, in particular. It is clear that if this effect is disregarded in the case of semiconductor QDs in dielectrics, e.g., the silicon QDs in silicon dioxide, and the results of the calculations for the energy characteristics of electron–hole pairs can be affected profoundly. In this paper, we report the calculations of the basic characteristics of excitons in spherical QDs. The calculations involve, in the firs
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