Slow light in Germanium nanocrystals
Author
Keleş, Ümit
Advisor
Bulutay, Ceyhun
Date
2009Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
The phenomena of quantum coherence has been applied with great success in
the atomic systems. For optoelectronic applications the interest is inherently directed
towards the semiconductor heterostructures. Large number of works have
proposed and analyzed the atomic quantum coherence effects in the semiconductors.
In this respect, nanocrystals (NCs) are very promising structures for seeking
the quantum coherence phenomena due to their atomic-like electronic structure.
Furthermore, their robust structure, integrability and larger excitonic lifetimes
with respect to atomic systems makes them more promising candidates for the
technological applications.
Within an atomistic pseudopotential electronic structure framework, the optical
Bloch equations (OBEs) originating from atomic coherence theory are derived
and solved numerically for Ge NCs. The results are interpreted in the context of
coherent population oscillations (CPO). Narrow dips are observed in the absorption
profiles which corresponds to high dispersions within a transparency window
and produce slow light. A systematic study of the size-scaling of slow-down factor
with respect to NC diameter and controllable slow light by applying external
Stark field are provided. The results indicate that Ge NCs can be used to generate
optically and electrically controllable slow light.
The many-body Coulomb interactions which underlie the quantum coherence
and dephasing are of central importance in semiconductor quantum confined systems.
The effects of many-body interactions on the optical response of Ge NCs
have been analyzed. The semiconductor optical Bloch equations (SBEs) are derived
in a semiclassical approach and the Coulomb correlations are included at
the level of Hartree-Fock approximation.
Keywords
Ge NanocrystalsSemiconductor Bloch Equations
Second Quantization
Radiative Recombination Times
Slow Light
Optical Bloch Equations
Density Matrix Formalism