Search

AbstractElectron structure of a silicon quantum dot doped with a shallow hydrogen-like donor has been calculated for the electron states above the optical gap. Within the framework of the envelope-function approach we have calculated the fine splitting of the ground sixfold degenerate electron state as a function of the donor position inside the quantum dot. Also, dependence of the wave functions and energies on the dot size was obtained.

Within the framework of the time-dependent density functional theory, the radiative recombination rates have been calculated for small, ∼ 1 nm in diameter, hydrogen-passivated silicon crystallites with a single lithium or phosphorus ion. Sharp increase of the radiative recombination rates with increasing temperature was revealed for the crystallites with the lithium ion. No temperature effect was found for the crystallites with the ion of P. It was also shown that the presence of ionized donors in Si crystallites can substantially accelerate the radiative decay compared to the case of pure crystallites. [ABSTRACT FROM AUTHOR]

In this review, we discuss several fundamental processes taking place in semiconductor nanocrystals (quantum dots (QDs)) when their electron subsystem interacts with electromagnetic (EM) radiation. The physical phenomena of light emission and EM energy transfer from a QD exciton to other electronic systems such as neighbouring nanocrystals and polarisable 3D (semi-infinite dielectric or metal) and 2D (graphene) materials are considered. In particular, emission decay and FRET rates near a plane interface between two dielectrics or a dielectric and a metal are discussed and their dependence upon relevant parameters is demonstrated. The cases of direct (II–VI) and indirect (silicon) band gap semiconductors are compared. We cover the relevant non-radiative mechanisms such as the Auger process, electron capture on dangling bonds and interaction with phonons. Some further effects, such as multiple exciton generation, are also discussed. The emphasis is on explaining the underlying physics and illustrating it with calculated and experimental results in a comprehensive, tutorial manner. [ABSTRACT FROM AUTHOR]

Ab initio study of Si crystallites (diameter: 1.1–2.4 nm) with fully Cl- or Br-passivated surfaces was performed. It was shown that halogenation straightens the band structure of such small Si nanocrystals in the momentum space, but it strongly separates the electron densities of states above and below the fundamental gap in real space. This causes a substantial slowdown (up to several orders of magnitude in the rates as compared to those in H-passivated nanocrystals) of the radiative electron–hole transitions, the rates of which were computed by using time-dependent density functional theory calculations. A similar effect takes place for Auger recombination—the rates of the Auger process become one–two orders of magnitude smaller as compared to those observed with hydrogen passivation. In contrast to radiative and Auger recombinations, the process of multiexciton generation is not, in fact, strongly affected by halogen surface passivation. This yields an essential rise in the internal quantum efficiency (up to the values close to 2 at its maximum) of multiexciton generation. This rise facilitates the consideration of halogenated Si nanocrystals as very attractive tools for photovoltaics applications. [ABSTRACT FROM AUTHOR]

Dissipative electron dynamics in a double quantum dot, influenced by external ac and dc electric fields, has been analyzed. It was shown that the dissipation caused by phonon environment disappears under certain relations between electric field parameters. In this case one may perform the dynamic localization and form stable electron states localized within one of the dots. [ABSTRACT FROM AUTHOR]

Abstract: Theoretical study of the chemical shift and ground level splitting in spherical silicon quantum dot with a shallow donor has been carried out within the framework of the method. We have found the great value of the chemical shift compared to the one in bulk. It is shown that the level splitting strongly depends on the dot radius and the donor position inside the nanocrystal. [Copyright &y& Elsevier]