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Temporal Dynamics of Magnetically Do...

Tarasek, Steven.

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Temporal Dynamics of Magnetically Doped Low Dimensional Semiconductor Structures.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Temporal Dynamics of Magnetically Doped Low Dimensional Semiconductor Structures./
Author:	Tarasek, Steven.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2021,
Description:	112 p.
Notes:	Source: Dissertations Abstracts International, Volume: 82-09, Section: B.
Contained By:	Dissertations Abstracts International82-09B.
Subject:	Physics. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28314421
ISBN:	9798582508861

Temporal Dynamics of Magnetically Doped Low Dimensional Semiconductor Structures.
Tarasek, Steven.

Temporal Dynamics of Magnetically Doped Low Dimensional Semiconductor Structures. - Ann Arbor : ProQuest Dissertations & Theses, 2021 - 112 p.

Source: Dissertations Abstracts International, Volume: 82-09, Section: B.

Thesis (Ph.D.)--State University of New York at Buffalo, 2021.

This item must not be sold to any third party vendors.

Through this thesis, I have introduced low dimensional semiconductor structures and examined how they behave when magnetic ions are embedded into the structures. The carrier dynamics of the low dimensional systems show different dynamics dependent on the presence of magnetic ions, leading to the new observations discussed.In chapter 1, I introduce the concept of the exciton, and explore how reduced dimensionality changes the density of states, leading to the development of quantum dots and nanoplatelets. The origin of magnetic spin exchange interactions is then introduced, as this plays a critical role in the results shown in the later chapters.Chapter 2 introduces the experimental method of time resolved photoluminescence which was utilized in order to study our magnetic semiconductor structures. For time resolved photoluminescence measurements, it is necessary to have a pulsed laser and a system which can temporally analyze light. I go through the fundamental operating principles of our Coherent Mira 900/RegA 9000/OPA 9400 system which is used to generate, amplify, and tune laser pulses along with the operating principles of our streak camera system and data analysis necessary for understanding the results of our experiments.Chapter 3 focuses on the Coulomb induced recombination dynamics in magnetically doped type-II quantum dots.I observe that the wavefunction overlap of the carriers in type-II quantum dots (QDs) can be controlled by magnetic doping and strongly depends on the excitation power density ($P_\extrm{ex}$). I study two different II-VI magnetic systems; ZnTe/(Zn,Mn)Se QDs with magnetic dopants in the matrix surrounding the dots, and (Zn,Mn)Te/ZnSe QDs doped in the dot core. Both magnetic systems, regardless of the location of the dopant magnetic ions, show a stark contrast in their emission with high excitation power densities when compared to nonmagnetic ZnTe/ZnSe QDs. Using time-resolved photoluminescence (TRPL), I observe a saturation in the blue shift for the magnetic systems at a lower $P_\extrm{ex}$, while additionally exhibiting a limited lifetime shortening over the entire range of $P_\extrm{ex}$, when compared to the nonmagnetic QDs. The results for the two magnetic systems are very similar, showing no dependence on the location of the magnetic impurities. This suggests that the behavior observed is an effect of the magnetic polaron on the band bending in the high $P_\extrm{ex}$ regime. The ability to use magnetic ions to quickly saturate the charge concentration and control band bending in QDs could potentially aid in optimizing optoelectronic devices which are sensitive to high charge variations.Chapter 4 explores switchable excitonic polarization in core/shell magnetic nanoplatelets. I utilized time-resolved photoluminescence spectroscopy to study the excitonic circular polarization from CdSe/CdMnS core/shell NPLs with a bilayer core. This allows an extensive study of the emission dynamics as a function of magnetic field, temperature, doping concentration, and excitation wavelength. In the presence of an external magnetic field, pulsed excitation below the shell gap results in near-zero excitonic circular polarization at all time delays. In contrast, pulsed excitation with photon energy larger than the shell gap results in a rapid (100 ps) buildup of the excitonic circular polarization which subsequently remains constant at a level of up to 40\\%. I propose a model to describe the dynamics which takes into account the exchange interaction between carrier and magnetic ion (Mn) spins. The studied system exhibits a fast switchable excitonic circular polarization, implying possible applications in lasers and light emitting diodes.

ISBN: 9798582508861Subjects--Topical Terms:

516296
Physics.
Subjects--Index Terms:

Exchange interaction

Temporal Dynamics of Magnetically Doped Low Dimensional Semiconductor Structures.
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245 1 0 $a Temporal Dynamics of Magnetically Doped Low Dimensional Semiconductor Structures.
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300 $a 112 p.
500 $a Source: Dissertations Abstracts International, Volume: 82-09, Section: B.
500 $a Advisor: Thomay, Tim.
502 $a Thesis (Ph.D.)--State University of New York at Buffalo, 2021.
506 $a This item must not be sold to any third party vendors.
520 $a Through this thesis, I have introduced low dimensional semiconductor structures and examined how they behave when magnetic ions are embedded into the structures. The carrier dynamics of the low dimensional systems show different dynamics dependent on the presence of magnetic ions, leading to the new observations discussed.In chapter 1, I introduce the concept of the exciton, and explore how reduced dimensionality changes the density of states, leading to the development of quantum dots and nanoplatelets. The origin of magnetic spin exchange interactions is then introduced, as this plays a critical role in the results shown in the later chapters.Chapter 2 introduces the experimental method of time resolved photoluminescence which was utilized in order to study our magnetic semiconductor structures. For time resolved photoluminescence measurements, it is necessary to have a pulsed laser and a system which can temporally analyze light. I go through the fundamental operating principles of our Coherent Mira 900/RegA 9000/OPA 9400 system which is used to generate, amplify, and tune laser pulses along with the operating principles of our streak camera system and data analysis necessary for understanding the results of our experiments.Chapter 3 focuses on the Coulomb induced recombination dynamics in magnetically doped type-II quantum dots.I observe that the wavefunction overlap of the carriers in type-II quantum dots (QDs) can be controlled by magnetic doping and strongly depends on the excitation power density ($P_\extrm{ex}$). I study two different II-VI magnetic systems; ZnTe/(Zn,Mn)Se QDs with magnetic dopants in the matrix surrounding the dots, and (Zn,Mn)Te/ZnSe QDs doped in the dot core. Both magnetic systems, regardless of the location of the dopant magnetic ions, show a stark contrast in their emission with high excitation power densities when compared to nonmagnetic ZnTe/ZnSe QDs. Using time-resolved photoluminescence (TRPL), I observe a saturation in the blue shift for the magnetic systems at a lower $P_\extrm{ex}$, while additionally exhibiting a limited lifetime shortening over the entire range of $P_\extrm{ex}$, when compared to the nonmagnetic QDs. The results for the two magnetic systems are very similar, showing no dependence on the location of the magnetic impurities. This suggests that the behavior observed is an effect of the magnetic polaron on the band bending in the high $P_\extrm{ex}$ regime. The ability to use magnetic ions to quickly saturate the charge concentration and control band bending in QDs could potentially aid in optimizing optoelectronic devices which are sensitive to high charge variations.Chapter 4 explores switchable excitonic polarization in core/shell magnetic nanoplatelets. I utilized time-resolved photoluminescence spectroscopy to study the excitonic circular polarization from CdSe/CdMnS core/shell NPLs with a bilayer core. This allows an extensive study of the emission dynamics as a function of magnetic field, temperature, doping concentration, and excitation wavelength. In the presence of an external magnetic field, pulsed excitation below the shell gap results in near-zero excitonic circular polarization at all time delays. In contrast, pulsed excitation with photon energy larger than the shell gap results in a rapid (100 ps) buildup of the excitonic circular polarization which subsequently remains constant at a level of up to 40\\%. I propose a model to describe the dynamics which takes into account the exchange interaction between carrier and magnetic ion (Mn) spins. The studied system exhibits a fast switchable excitonic circular polarization, implying possible applications in lasers and light emitting diodes.
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650 4 $a Quantum physics. $3 726746
650 4 $a Nanoscience. $3 587832
653 $a Exchange interaction
653 $a Magnetism
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653 $a Nanostructures
653 $a Quantum dots
653 $a Time resolved photoluminescence
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710 2 $a State University of New York at Buffalo. $b Physics. $3 1025831
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