Optical absorption in semiconductor quantum dots: A tight-binding approach

Ramaniah, Lavanya M.; Nair, Selvakumar V.

doi:10.1103/physrevb.47.7132

Cited by 112 publications

(66 citation statements)

References 26 publications

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“…The calculated values are a factor of 5 larger than the experimentally found values. The oscillator strength has also been calculated by Ramaniah and Nair [36] by a tight binding approach and was found to be 4.9 for a radius of 2.07 nm for spherical CdSe quantum dots. However, qualitatively in all cases a weak dependence on emission energy is found that slightly decreases for higher emission energy, in agreement with our results.…”

Section: Discussionmentioning

confidence: 99%

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Size-dependent oscillator strength and quantum efficiency of CdSe quantum dots controlled via the local density of states

et al. 2009

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We study experimentally time-resolved emission of CdSe quantum dots in an environment with a controlled local density of states (LDOS). The decay rate is measured versus frequency and as a function of distance to a mirror. We observe a linear relation between the decay rate and the LDOS, allowing us to determine the size-dependent quantum efficiency and oscillator strength. We find that the quantum efficiency decreases with increasing emission energy mostly due to an increase in nonradiative decay. For the first time, we manage to obtain the oscillator strength of the important class of CdSe quantum dots. The oscillator strength varies weakly with frequency in agreement with behavior of quantum dots in the strong confinement limit. Surprisingly, the measured absolute values are a factor of 5 below theoretically calculated values. Our results are relevant for applications of CdSe quantum dots in spontaneous emission control and cavity quantum electrodynamics. * URL: www.photonicbandgaps.com arXiv:0808.3191v1 [physics.optics]

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Section: Discussionmentioning

confidence: 99%

“…b) Quantum efficiency for different emission energies. c) Oscillator strength for different emission energies together with a model describing a strongly confined quantum dot (equation 7) and results from tight binding calculations [36].…”

Section: Discussionmentioning

confidence: 99%

Size-dependent oscillator strength and quantum efficiency of CdSe quantum dots controlled via the local density of states

et al. 2009

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“…In ab initio theories, [6][7][8][9][10] one can use minimal coupling ͑with suitable modifications for nonlocal potentials 11 ͒ and calculate directly the necessary matrix elements of the momentum or velocity operator. In the empirical theory, these matrix elements can simply be treated as extra fitting parameters, [12][13][14][15] determined by fitting the dielectric function ͑and thus oscillator strengths͒ to experimental or first-principles spectra. However, even with the full use of symmetry restrictions, the number of additional parameters can be undesirably large; for example, Chang and Aspnes 13 where x is the coordinate of the electron and H is the Hamiltonian.…”

Section: Introductionmentioning

confidence: 99%

Consequences of local gauge symmetry in empirical tight-binding theory

Foreman

2002

Phys. Rev. B

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A method for incorporating electromagnetic fields into empirical tight-binding theory is derived from the principle of local gauge symmetry. Gauge invariance is shown to be incompatible with empirical tight-binding theory unless a representation exists in which the coordinate operator is diagonal. The present approach takes this basis as fundamental and uses group theory to construct symmetrized linear combinations of discrete coordinate eigenkets. This produces orthogonal atomiclike ''orbitals'' that may be used as a tight-binding basis. The coordinate matrix in the latter basis includes intra-atomic matrix elements between different orbitals on the same atom. Lattice gauge theory is then used to define discrete electromagnetic fields and their interaction with electrons. Local gauge symmetry is shown to impose strong restrictions limiting the range of the Hamiltonian in the coordinate basis. The theory is applied to the semiconductors Ge and Si, for which it is shown that a basis of 15 orbitals per atom provides a satisfactory description of the valence bands and the lowest conduction bands. Calculations of the dielectric function demonstrate that this model yields an accurate joint density of states, but underestimates the oscillator strength by about 20% in comparison to a nonlocal empirical pseudopotential calculation.

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“…The fact that the gap shows an overall decrease with increasing cluster size has also been found by other groups. [23,32,33,64,65] The gap size is drawn as a function of 1 -n -1/2 (n being the number of CdS pairs) for unrelaxed clusters in Figure 6. This plot accentuates the size dependence of the gap.…”

Section: Electronic Structurementioning

confidence: 99%

The Effects of Organisation, Embedding and Surfactants on the Properties of Cadmium Chalcogenide (CdS, CdSe and CdS/CdSe) Semiconductor Nanoparticles

et al. 2005

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An overview of recent density‐functional‐based studies on the structure, surface structure and electronic and optical properties of CdS, CdSe and CdS/CdSe semiconductor nanoparticles is given. In particular, the effects of organisation, embedding and surfactants on the properties of these particles are discussed and illustrated by our own results and literature examples. The surface stabilisation by ligands, core/shell embedding or superstructure organisation combined with electronic structure stabilisation of these nanoparticles directly influences their properties: for stabilised nanoparticles a size‐dependent decay of the lowest optical excitation energy towards the value of the bulk is found, as observed experimentally. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

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Optical absorption in semiconductor quantum dots: A tight-binding approach

Cited by 112 publications

References 26 publications

Size-dependent oscillator strength and quantum efficiency of CdSe quantum dots controlled via the local density of states

Size-dependent oscillator strength and quantum efficiency of CdSe quantum dots controlled via the local density of states

Consequences of local gauge symmetry in empirical tight-binding theory

The Effects of Organisation, Embedding and Surfactants on the Properties of Cadmium Chalcogenide (CdS, CdSe and CdS/CdSe) Semiconductor Nanoparticles

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