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POLARIZATION COUPLING IN SEMICONDUCTOR NANO-DIMERS IN THE TERAHERTZ RANGE
Title
POLARIZATION COUPLING IN SEMICONDUCTOR NANO-DIMERS IN THE TERAHERTZ RANGE
Creator
Hu, Zhijing
Date
2017, 2017-05
Description
Surface plasmon resonance (SPR) occurs at the interface of a semiconductor and a dielectric when certain conditions are satisfied. SPR is...
Show moreSurface plasmon resonance (SPR) occurs at the interface of a semiconductor and a dielectric when certain conditions are satisfied. SPR is impetus to new sensor and device development in the optical range, with nanoparticles of noble metals taking up major roles. Typical conduction band electron concentrations in semiconductors lead to resonance frequencies in the terahertz and infrared bands. While the response strength is weaker than those exhibited by metals, it can be made up for by the formation of aggregates. The added degree of freedom by doping or carrier injection further enhances the versatility of semiconductor nanoclusters. To obtain a first principle solution to the coupled set of equations for charge carrier transport and electrodynamics in a conductive cluster is a formidable task with a high computational cost. Employing a finite-element based tool, the COMSOL Multiphysics Simulation Software, the interaction inside and outside some elementary semiconductor structures such as slab and sphere have been solved, which revealed the screening of the internal field while displaying dispersion and absorptions effects. The study of semiconductor dimer also showed a significant field enhancement and frequency shift. Under strong applied field, asymmetric polarization within the particles is revealed. The accompanying nonlinear polarization response can be employed to develop new devices. These model structures can serve to provide insight to the analysis and synthesis more complex structures.
Ph.D. in Electrical Engineering, May 2017
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PURIFICATION AND CRYSTAL GROWTH OF INI AND ALLOYS IN1-xTLxI AND IN1-xGAxI FOR APPLICATION IN X-RAY AND GAMMA-RAY DETECTORS
Title
PURIFICATION AND CRYSTAL GROWTH OF INI AND ALLOYS IN1-xTLxI AND IN1-xGAxI FOR APPLICATION IN X-RAY AND GAMMA-RAY DETECTORS
Creator
Riabov, Volodymyr
Date
2016, 2016-07
Description
The present work is focused on developing new semiconductor materials based on Indium Monoiodide (InI) for application in room temperature X...
Show moreThe present work is focused on developing new semiconductor materials based on Indium Monoiodide (InI) for application in room temperature X-ray and gamma-ray detectors. During past two decades InI was studied as room a temperature detector material due to suitable value of the energy gap and high atomic number of its constituents. The most recent studies include investigations at laboratories of Prof. A. Ostrogorsky at Rensselaer Polytechnic Institute (RPI) and Illinois Institute of Technology (IIT) during period 2009-2013. The present work was focused on (i) purification of starting InI material and (ii) crystal growth of InI and InI based alloys with objective to investigate effects of purification and alloying on crystal structure, electrical and mechanical properties. Purification was performed at Radiation Monitoring Devices (RMD) Inc. by innovative techniques combined with well established methods, such as Zone Refining Under Reactive Atmosphere. At RMD, purification was followed by crystal growth of InI by the travelling molten zone method. Crystal growth of InI and alloys In0.99Ga0.01I, In0.99Tl0.01I, In0.95Tl0.05I was performed by Vertical Gradient Freeze (VGF) Method at IIT. The microstructure of produced crystals was analyzed, and their Knoop micro-hardness was measured. The concentration of the dopants as a function of position along the crystals was analyzed by Glow Discharge Mass Spectrometry (GDMS) technique. Band gap of produced materials was estimated as a function of composition by Near-UV-Visible range spectroscopy. Radiation detectors were manufactured from produced crystals. Their electrical properties, such as resistivity, photosensitivity and charge carrier mobility, were measured and, finally, detection performance was estimated.
M.S. in Mechanical and Aerospace Engineering, July 2016
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Polarization Induced by a Terahertz Electric Field on a Core-shell Particle
Title
Polarization Induced by a Terahertz Electric Field on a Core-shell Particle
Creator
Li, Yanlin
Date
2018
Description
Interactions of an electromagnetic wave with a sphere that is smaller than the wavelength can be accounted for by studying the dipole moments,...
Show moreInteractions of an electromagnetic wave with a sphere that is smaller than the wavelength can be accounted for by studying the dipole moments, which are the valid explanation for the scattering characteristics in the frequency region known as the Rayleigh region. The semiconductor nanoparticle with a core-shell structure describes a specific geometry yielding tunable plasmon resonance of the nanostructure. This is achieved by varying the thickness of the dielectric material shell layer on a semiconductor core. The polarization of core-shell sphere induced by a dynamic field is studied both analytically and numerically. Dielectric function is used for the description of the response of bound charges to an applied field, resulting in the electric polarization, which has been employed to explicate scattering and absorption properties of particles over the years. However, this traditional model has some limitations in accounting for some aspects of polarization when mobile charges are present. By coupling the transport equations of the charge carriers to the Maxwell’s equations, we can derive the electric field, charge and the total induced dipole moment of a nano-core-shell particle. Results of calculations accomplished for elementary structures such as plates and spheres represented the screening of the internal field while dispersion and absorptions effects are revealed by the complex dipole moments. And the results in static and quasi-static field are shown. Equivalent circuits for the core-shell structures are obtained from carrier transport consideration, which can be employed to guide the synthesis of new nanoparticles with heterogeneous internal structures to achieve novel polarization properties for sensing and terahertz circuitry applications.
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