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Title: Modelling of silicon-germanium alloy heterostructures using double group formulation of k . p theory
Author: Ward, Robert M.
ISNI:       0000 0004 2724 1234
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2012
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Silicon-Germanium alloy heterostructures offer the most viable opportunity to integrate electronics with optoelectronic devices for widespread commercial application. Indeed Germanium rich devices may be designed for application around 1.5 m by preying on the direct-gap energy of 890meV. Low power optical modulators operating, under the quantum confined Stark effect, at wavelength bands used in 3rd generation fibre optic communication channels are developed in this thesis from a theoretical perspective. An investigation into strained Germanium rich quantum well structures was performed, revealing information about sub-band dispersion, joint density of states and absorption coefficient using the double group formulation of k . p theory. Using zone centre eigenstates as symmetrised half integer basis functions transforming according to irreps of the double group, the spin orbit interaction is incorporated into the unperturbed Hamiltonian. Along with semi-empirical input parameters available in the literature, dispersion in bulk Silicon and Germanium reveals information about hole effective masses and indirect conduction band minima in broad agreement with experimental data. In accordance with degenerate perturbation theory; effective mass Hamiltonians, with an arbitrary quantisation axis through a canonical transformation, are constructed through a series of matrix multiplications. Retaining operator ordering allows numerical modelling of heterostructures grown on arbitrary growth planes with appropriate boundary conditions across an abrupt interface under the envelope function framework. In this thesis, the effect on the transition energy, hh1-e1, by the choice of growth plane in a quantum well heterostructure is investigated.
Supervisor: Zhang, Jing ; Stavrinou, Paul Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral