| The continuous progress in epitaxial growth and patterning technology offers today unprecedented possibilities to fabricate nanosize semiconductor heterostructures which exhibit quantum confinement of charge carriers in three spatial dimensions.; Theoretical calculations of the electronic properties of semiconductor quantum dots, as presented in this work, are important since they provide valuable information for designing quantum dot-based optoelectronic devices, such as infrared photodetectors and quantum-dot lasers. Complex numerical models are prerequisite for the simulation of the non-trivial impact of the real structure (e.g., shape, chemical composition, inhomogeneous strain, etc.) on the electronic and optical properties, eventually leading to a comprehensive understanding of the manifold of experimental data available. Quantitatively correct theoretical predictions will also ultimately provide guidance to tailor the properties of optoelectronic devices based on self-assembled quantum dots.; The realization of this potential depends on the power of the theoretical model. It is commonly agreed that the inhomogeneous strain inherently connected to the formation of strained quantum dots, e.g., within the (In,Ga)As/GaAs material systems, strongly influences their electronic structure. Band mixing effects, being caused by confinement in general and enhanced by reduced dimensionality and by strain effects, are of equal significance. These insights promoted the use of perturbation and multiband models in which the strain effects are taken into consideration, so that the numerical implementations would allow one to treat realistic geometrical and chemical properties of the dots.; The k•p model provides, at reasonable computational cost, a fast and transparent connection between the electronic structure of quantum dots and certain bulk properties of the constituent materials, making it easier to take into account arbitrary quantum dot shapes and material compositions, as well as strain and band mixing. This renders the eight-band k•p model attractive for a realistic analysis of quantum-dot structures.; In this work, eight-band k•p theory including strain is applied to calculation of electronic properties of strained (In,Ga)As/GaAs quantum dots of pyramidal and truncated pyramidal shape. The approximate shape of the dots and the main dimensions of the dots are extracted from cross-sectional high-resolution transmission electron microscopy analysis. The electronic structure, the interband emission spectra, and the intraband absorption spectra are calculated within one coherent framework. As it is mandatory to assume realistic bulk properties of the constituent semiconductor materials, the bandstructures near the Brillouin zone center are described by the eight-band k•p Kane model including the conduction band, as well as the heavy hole, light hole, and spin-orbit split off valence bands.; The specific heterostructures treated in this work are self-organized (In,Ga)As quantum dots embedded in a GaAs matrix, as well as InAs quantum dots embedded in InGaAs quantum-well structures, grown by molecular beam epitaxy, in Stranski-Krastanow growth mode. The electronic and optical properties of these lattice-mismatched heterostructures are strongly influenced by pseudomorphic strain. The effects of inhomogeneous strain on the band structure of bulk semiconductors are included via deformation potential theory, as proposed by Pikus and Bir. To calculate the strain field within the quantum dots, an analytical model based on Eshelby's classical inclusion theory is developed in this work.; The overall intention of this work is to establish and validate an all-numerical treatment allowing a flexible modeling of a variety of low-dimensional nanostructures. Comparisons to various experiments, such as Photoluminescence Spectroscopy and Fourier Transform Infrared Spectroscopy,... |
