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Title: Spectroscopic studies of quantum dot intersublevel transitions in the few terahertz frequency range
Author: Porter, Nathan Edward
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2013
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This thesis presents intraband optical studies of self-assembled quantum dots (QDs) in the few terahertz (THz) range and optical THz frequency mixing in the same samples. Magneto-transmission measurements of QDs in the few-terahertz range are described. The polaronic nature of the excitations of the system was studied by tracking the intraband transition energy as a function of magnetic field up to 28T. The first direct measurement of anticrossings in the I-LO phonon energy range are reported and evidence of polarons consisting of an electron bound with an InAs-like optical phonon in addition to phonon-like polarons is presented. Degenerate pump-probe spectroscopy was used to study intraband energy relaxation for transition energies below the LO phonon energy. Post-growth annealing was used to reduce the energy level separation of the samples to below the typical as-grown transition energy of 40 - 60me V. It was observed that as the intraband transition energy reduced, the relaxation times increased, exhibiting very strong energy dependence. It was found that at an energy of ~ 30meV (7THz) the relaxation times were of the order of 2ps, whilst at an energy of ~ 14meV (3.4THz) the relaxation times increased to 1.5ns. These results were explained using a microscopic polaron relaxation model (developed by colleagues at the ENS, Paris), in which decay occurs via phonon anharmonicity, with very good agreement found between experiment and theory. Optical sideband generation via frequency mixing of a near infrared (NIR) laser beam and a THz beam using interband and intraband resonances in QDs is described.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available