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Type of Document Dissertation Author Titova, Lyubov Author's Email Address ltitova@nd.edu URN etd-12142004-153155 Title OPTICAL STUDIES OF LOW DIMENSIONAL MAGNETIC AND NON-MAGNETIC SEMICONDUCTOR STRUCTURES Degree Doctor of Philosophy Department Physics Advisory Committee
Advisor Name Title Patricia Clark Committee Chair John LoSecco Committee Member Kathie Newman Committee Member Malgorzata Dobrowolska Committee Member Morten Eskildsen Committee Member Keywords
- semiconductor nanostructures
- optical properties of semiconductors
- magnetic semiconductors
Date of Defense 2004-06-23 Availability restricted Abstract The focus of this thesis is on optical studies of the properties ofsemiconductor heterostructures fabricated by the molecular beam
epitaxy.
ZnCdSe quantum wells were grown on the cleaved (110) edge of
ZnCdSe/ZnSe multiple quantum well structures with the intent of
creating T-shaped quantum wires at intersections of the quantum
wells. Extensive polarization-dependent micro-photoluminescence
studies were carried out on all the samples. We report the
observation of the photoluminescence emission from the quantum
wire in one of the samples. The absence of the quantum wire
photoluminescence lines in other samples may be caused by the
roughness of the interfaces formed by ZnCdSe deposition on the
cleaved (110) surface which can affect the quality of the
T-junctions formed by the intersection of the quantum wells. In
addition to preliminary success in fabricating ZnCdSe quantum
wires in the ZnSe matrix, this work has also resulted in the
observation of zero-dimensional ZnSe/ZnCdSe quantum structures (
natural quantum dots). The natural quantum dots result from the
carrier localization on the fluctuations of the thickness of the
ZnCdSe quantum wells grown on (110) cleaved surface due to (110)
interface roughness.
We also describe the properties of self-assembled CdSe quantum
dots grown on Mn-passivated ZnSe buffers. We show that the Mn
deposited on the ZnSe surface acts as a nucleating seed for
self-assembled QD formation. At certain optimal growth conditions,
the presence of Mn on ZnSe surface results in a significant
improvement in size uniformity compared to CdSe dots grown on ZnSe
without Mn passivation as evidenced by photoluminescence as well
as transmission electron microscopy experiments. We also show that
the dots exhibit large Zeeman splitting observed in the
photoluminescence emission, indicating that this growth method is
suitable for fabricating magnetic quantum dots that exhibit strong
spin polarization effects.
In addition to our studies of the II-VI semiconductor
heterostructures, we have investigated the magnetic properties of
ferromagnetic GaMnAs, GaMnSb, and InMnSb grown on hybrid
GaAs/II-VI substrates by the magneto-optical Kerr effect and
magnetic circular dichroism measurements. The results of the
magneto-optical experiments were compared with those obtained by
direct magnetization measurements and electrical transport.
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