Dissertation/Thesis Abstract

Ultrafast Exciton Dynamics and Optical Control in Semiconductor Quantum Dots
by Wijesundara, Kushal Chinthaka, Ph.D., Ohio University, 2012, 124; 10631469
Abstract (Summary)

Device miniaturization with advanced fabrication techniques has revolutionized the semiconductor industry along with innovative concepts of carrier spin, potentially important at the fundamental physical limits of scalability. For spin-based information processing, semiconductor coupled quantum dots (CQDs) provide excellent control in spin dynamics due to 3-D confinement, discrete energy levels, and optical orientation and coupling. The research presented in this dissertation investigates spin interactions and exciton relaxation channels in semiconductor CQDs measured through optical control and time-resolved experimental techniques.

Our experiments involving photoluminescence (PL) and photoluminescence excitation (PLE) methods revealed effects arising from the structural properties of semiconductor nanostructures, including quantum rings and CQDs. High resolution PL measurements on positively charged exciton states demonstrated experimental evidence of isotropic exchange interaction. Controlling exchange interaction in different spin configurations is fundamental to quantum logic operations. Hence, polarization dependent PL experiments were executed and electric field tunable exchange interaction effects were reported on the neutral exciton states.

Next, time-resolved measurements were performed while pumping above the InAs wetting layer (WL) energy and probing below the WL to determine the dynamics of the optically generated electric field in CQDs. The observed, rapid onset of the optically generated electric field may provide the use of CQDs for optical switching applications.

Finally, carrier relaxations in the CQDs were identified through the dynamics of the spatially indirect exciton state using a mode-locked laser excitation source and standard time-resolved single photon counting technique. Wave function distribution, carrier tunneling, and phonon scattering led to the observed lifetime and intensity modulations. With time-resolved PLE, bi-exponential lifetime decay revealed non-monotonic phonon relaxations as a result of the structure factor of the CQDs. Furthermore, with resonant excitation, carrier tunneling into charged exciton states was also eliminated. These results demonstrated tunable exciton relaxation rates in CQDs, which are useful for quantum information, optoelectronics, and photonics applications.

Indexing (document details)
Advisor: Stinaff, Eric A.
Commitee: Govorov, Alexander, Hla, Saw-Wai, Rack, Jeffrey
School: Ohio University
Department: Physics and Astronomy
School Location: United States -- Ohio
Source: DAI-B 78/11(E), Dissertation Abstracts International
Subjects: Molecular chemistry, Nanoscience, Quantum physics, Physics, Molecular physics, Condensed matter physics, Nanotechnology, Materials science
Keywords: Coupled quantum dots, Nanophotonics, Photovoltaics, Semiconductor quantum dots, Time-resolved photoluminescence, Ultrafast optics
Publication Number: 10631469
ISBN: 9780355016918
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