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Title: Long wavelength spectroscopy of charge dynamics and spin dependent processes in optoelectronic materials
Author: Clarke, Damien Geoffrey
ISNI:       0000 0001 3557 4424
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 2003
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The experiments presented in this thesis investigated charge and spin dynamics within optoelectronic materials with long wavelength spectroscopy. The majority of the studies involved using a Free Electron Laser (FEL) to reach long wavelengths (~1 mum to ~100 mum) with a high power. Several two-colour time resolved experiments with the FEL and a Ti:Sapphire laser have, also, been conducted. Through the use of a double resonance technique it has been discovered that indium profile fluctuations cause inhomogeneous broadening of the PL in InAs/GaAs quantum dots. Annealing the dots was discovered to reduce this inhomogeneity. Two experiments studied the dynamics of excitons within GaAs/AlGaAs quantum wells. The Dynamic Franz Keldysh Effect was observed by using an FEL to apply an intense THz field. By using time resolved spectroscopy the contention that observing PL at the exciton energy necessarily implies that excitons are present has been challenged. This showed the characteristic 1s-1p exciton absorption to be absent for at least 500 ps when excitons were created through continuum pumping, however, PL was observed at the exciton frequency with a rise time of only ~570 ps. A high-pressure gas system was used to study the recombination mechanisms within InAs LEDs. It was found that Auger recombination mechanisms were dominant in type II structures while radiative recombination may be dominant in type I structures. Spin dependent processes have been studied within GaAs/AlGaAs quantum wells in two ways. Firstly, using a circularly polarised pump beam to create a spin biased carrier population, then measuring an induced, Faraday rotation upon reflection from the sample lead to the conclusion that the D'yakonov-Perel spin relaxation mechanism was dominant. Secondly, the Circular Photocurrent Galvanic Effect and the Spin Galvanic Effect have been investigated. Both cause a current to flow due to a spin related asymmetry in the carrier distribution.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available