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Title: Saturation of Intersubband Transitions in p-type and N-type III-V Qua'ntum Wells
Author: Steed, Robert John
ISNI:       0000 0001 3478 7575
Awarding Body: Imperial College London (University of London)
Current Institution: Imperial College London
Date of Award: 2007
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Intersubband transitions (ISBTs) in quantum wells have had extensive prior research but remain interesting. This thesis continues the use of saturation experiments for the characterisation of ISBT relaxation times ie. the time taken for carriers to scatter between a quantum well's subbands. Saturation experiments were carried out using an optical parametric generator as a tunable source of mid-infrared laser light (6.4 --t 8.6 pm) and intensities of -200MWcm-2 were reached. For this thesis, two p-doped samples were saturated, each sample containing multiple GaAs/AIGaAs quantum wells. Both sample's quantum wells had two confined heavy hole levels and the ISBTs between them, had energies of 160meV and 183meV (respectively). The hhl-hh2 ISBTs were saturated for each sample, the measured carrier relaxation times were 0.3 ± 0.1 ps and 2 ± 1.4 ps respectively, indicating that relaxation occurred via LO phonon emission (for comparison, an n-type quantum well with an ISBT of similar energy would have a relaxation time between 0.3 --t 0.6 ps). The effect of circularly polarised light on the carrier dynamics ofn-doped GaAs/AIGaAs quantum wells was also investigated. Circularly polarised light can lead to spin-sensitive ISBTs; this has been shown to lead to a change in the ISBT's saturation intensity for circularly polarised light due to the addition of the spin-relaxation time to the carrier dynamics. For this thesis, saturation experiments were performed using light incident at an oblique incidence to the QWs (via a novel sample geometry) but no significant differences in saturation intensity were {ound between using circularly and linearly polarised light.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available