Optical and Electronic Correlation Effects in Semiconductor Nanostructures with Emphasis on Silicon Nanostructure
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2011-04
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Addis Ababa University
Abstract
In this thesis we theoretically investigated static and dynamic correlation effects in semiconductor nanostructures. Structural inhomogneity and confinement quantization effects make this class of materials exhibit exotic properties under different experimental conditions. Time dependent coupling of the local states under time dependent perturbations and the fluctuation of the proximity couplings in the length scale of tunneling give rise to dynamical correlations that put their signature in the optical and transport properties. Based on the Orbital Free Local Density Approximation (OF-LDA), the exchange and correlation contribution to the orbital energy and the size dependent nature of the threshold for optical absorption are studied. The effects of dynamical correlations between the states in a single nanostructure and the effects of dynamical correlations between the states in proximity coupled configurations are investigated with the Non Equilibrium Green Function Formalism (NEGF) as the theoretical frame work.
The theoretical formulation of the non equilibrium dynamical analysis is used to describe the coherent regime optical and transport phenomena in semiconductor nanostructures. The results demonstrate that the presence of strong coupling between electronic states in semiconductor nanostructures leads to the formation of d states. First we have shown the emergence of collapse and revival phenomenon during the coherent regime absorption in a single dot. We presented qualitative and quantitative description of the Rabi oscillation. The dependence on the mean photon number and on the strength of the couplings between electronic states is demonstrated. We found that similar phenomenon in a wide range of many body system could be satisfactorily described assuming entanglement of the lower levels. Secondly, we theoretically investigated correlation effects in tunnel coupled nanostructures. The quantum blockade phenomenon in wide experimental samples is
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explored. The appearance of double dot structures as a time shared entangler is predicted. It is also found that the presence of a transparent boundary between quantum dots lead to the formation of local entangled states that are too difficult for experimental demonstration. Lastly the possible technological value of a double dot –in series configuration is presented. Its operation as electron-spin polarization is discussed and its potential for application as IR detector is proposed
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Optical and Electronic Correlation Effects