Properties of Type-II ZnTe/ZnSe Submonolayer Quantum Dots Studied via Excitonic Aharonov-Bohm Effect and Polarized Optical Spectroscopy

<p>In this thesis I develop understanding of the fundamental physical and material properties of type-II ZnTe/ZnSe submonolayer quantum dots (QDs), grown via combination of molecular beam epitaxy (MBE) and migration enhanced epitaxy (MEE). I use magneto-photoluminescence, including excitonic Aharonov-Bohm (AB) effect and polarized optical spectroscopy as the primary tools in this work.</p> <p>I present previous studies as well as the background of optical and magneto-optical processes in semiconductor nanostructures and introduce the experimental methods in Chapters 1 - 3.</p> <p>In Chapter 4 I focus on the excitonic AB effect in the type-II QDs. I develop a lateral tightly-bound exciton model for ZnTe/ZnSe type-II QDs, using analytical methods and numerical calculations. This explained the magneto-PL observation and allowed for establishing the size and density of the QDs in each sample based on the results of PL and magneto-PL measurements. For samples with larger QDs, I observe behaviors that fall between properties of quantum-dot and quantum-well-like systems due to increased QD densities and their type-II nature. Finally, the decoherence mechanisms of the AB excitons are investigated via the temperature dependent studies of the magneto-PL. It is determined that the AB exciton decoherence is due to transport-like (acoustic phonon) scattering of the electrons moving in the ZnSe barriers, but with substantially smaller magnitude of electron-phonon coupling constant due to relatively strong electron-hole coupling within these type-II QDs.</p> <p>In Chapter 5 I discuss the results of circularly polarized magneto-PL measurements. A model with ultra-long spin-flip time of holes confined to submonolayer QDs is proposed. The <em>g</em>-factor of type-II excitons was extracted from the Zeeman splitting and the <em>g</em>-factor of electrons was obtained by fitting the temperature dependence of the degree of circular polarization (DCP), from which <em>g</em>-factor of holes confined within ZnTe QDs was found. It is shown that it is about three times larger than that of bulk ZnTe.</p> <p>In Chapter 6 I study the optical anisotropy in QDs. I show that all samples exhibit such an effect, and explain it based on non-spherical shape of the QDs. Numerical calculation is applied to calculate degree of linear polarization, and estimate the aspect ratio. The exciton anisotropic exchange splitting is calculated from the magnetic field dependence of the DCP.</p> <p>In the last two chapters I show my achievement on the growth of ZnO nanorods as a core for type-II 1D systems and propose an outlook for future research on the type-II semiconductor heterostructures.</p>

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Physics

Grantor

The Graduate School and University Center of The City University of New York

Year dc:date.available

2016

Author dc:creator

• Ji, Haojie

Advisor dc:contributor.advisor

• Dr. Igor Kuskovsky

Committee members dc:contributor.committeemember

• Dr. Igor Kuskovsky
• Dr. Carlos Meriles
• Dr. Vinod M. Menon
• Dr. Lev Murokh
• Dr. Dmitry Smirnov

• Condensed Matter Physics
• Optics
• Type-II
• Quantum dots
• Aharonov-Bohm effect
• Polarized optical spectroscopy

Repository record dc:identifier

https://academicworks.cuny.edu/gc_etds/686

OAI identifier oai:identifier

oai:academicworks.cuny.edu:gc_etds-1687