InAs/GaAs QUANTUM RING IN ENERGY DEPENDENT PARTICLE EFFECTIVE MASS APPROXIMATION

Taqwanda Parson
Faculty Mentor: Dr. Igor Filikhin, Dr. Branislav Vlahovic

Three-dimensional InAs/GaAs quantum ring was studied under the energy dependent quasi-particle effective mass approximation. The confined energy problem was solved numerically by the finite element kp-perturbation method in a single subband approach. The influence of the quantum ring geometry on energy states and the electron effective mass ware investigated. The limits of applicability of the considered model are discussed.

InAs/GaAs QUANTUM RING IN ENERGY DEPENDENT PARTICLE EFFECTIVE MASS APPROXIMATION(.PDF)

PULSED LASER DEPOSITION OF MICROCRYSTALLINE SILICON

Justice McConnell
Faculty Mentor: Dr. Branislav Vlahovic

Microcrystalline silicon p-i-n solar cells are being proposed as the bottom cell in a-Si/µc-Si tandem solar cells for improved red absorption in the solar spectrum [1,2]. Thin film deposition of ?c-Si gained popularity after the report of ?c-Si:H single cells having a photo-stable conversion efficiency as high as 8 percent, with a short circuit current density over 25 mA/cm2. As per a recent modeling, efficiency as high as 16 percent with a short circuit current density of 33.5 mA/cm2 for single junction ?c-Si cells can be obtained for an optimum grain size of 1 µm and film thickness of 10 µm[3]. Fabrication of such a cell followed by tandem configuration with a-Si would greatly fulfill the goal of finding an efficient renewable energy source.

PULSED LASER DEPOSITION OF MICROCRYSTALLINE SILICON(.PDF)

PULSED LASER DEPOSITION OF MICROCRYSTALLINE SILICON FIGURE(.PDF)

NUMERICAL SIMULATION OF ELECTRONIC PROPERTIES IN QUANTUM DOT HETEROSTRUCTURES

Misty L. Green
Faculty Mentors: Dr. B. Vlahovic, Dr. I. Filikhin, and Dr. K Wang

A confined structure in all three dimensions leads to carrier’s discrete energy level spectrum in quantum dots. This property has profound impact on many applications, such as single electron transistors, quantum dot laser, high efficiency photovoltaic cells, information storage etc. A finite element method is utilized to model the residual stress distribution. The effect of residual stress on the electronic and optical properties is studied. This is accomplished by incorporating both the valence subbands and the strain-induced potential field into Schrodinger equation. A finite-difference method was applied to solve the equation system. The density of states is obtained from the spectrum of the eigenstates. The discrete eigenstate distributions for both with and without residual stress are compared. The effect of the quantum dot size and geometry to the energy state distribution is discussed.

NUMERICAL SIMULATION OF ELECTRONIC PROPERTIES IN QUANTUM DOT HETEROSTRUCTURES(.PDF)

PRECISION MEASUREMENT OF LOW LOSS WINDOW MATERIALS

Kiron Subaro
Faculty Mentor: Dr. Jyotsna M. Dutta

MA technique for measuring complex dielectric permittivity in the 118-178 GHz frequency range is suggested. The combination of a high-quality Fabry-Perot resonator, excited by a BWO-generator, with the great processing capability of a sensitive receiver, based on the Tektronix 2782 spectrum analyzer (using the WM782 (F-G) harmonic mixers), opens the possibility of a new measuring technique.
The dielectric losses are investigated on various materials, which include sapphire, high resistivity silicon, boron nitride, and CVD grown diamonds. Out of various techniques, Fabry-Perot resonator method has proven to be most convenient and accurate one. It provides the accuracy of the refractive index value close to 10-4 and scope to measure loss tangent (tand) value close to 10-6. Measurement scheme is described and some measurement values are reported.

PRECISION MEASUREMENT OF LOW LOSS WINDOW MATERIALS(.MS Word)

NUMERICAL MODELING OF RESIDUAL STRESSES AND THEIR EFFECTS ON THE ELECTRONIC AND OPTICAL PROPERTIES OF QUANTUM DOT SOLAR CELLS

Marcia Archibald
Faculty Mentor: Dr. Branislav Vlahovic

Quantum dots have been proposed as one of the promising technologies for solar cells that can provide a much higher efficiency. They are usually fabricated by growing nanometer sized semiconductor materials on various substrates. Due to differences in thermoelastic properties between quantum dots and the substrate materials, residual stresses will be generated in the quantum dots. The residual stresses will cause defects to be generated in the devices and consequently affect the electronic and optical properties. The finite element method has been applied to model the distribution of the residual stresses in quantum dots. The effects of the size, geometry, and fabrication temperature were investigated. The results provide further information for studying the effects of quantum dots on the electronic and optical properties of the solar cells.

NUMERICAL MODELING OF RESIDUAL STRESSES AND THEIR EFFECTS ON THE ELECTRONIC AND OPTICAL PROPERTIES OF QUANTUM DOT SOLAR CELLS(.MS Word)

RECRYSTALLIZATION OF AMORPHOUS Si BY LASER IRRADIATION

Justice McConnell
Faculty Mentor: Dr. Branislav Vlahovic Dr. and Jyotsna Dutta

Thin a-Si:H films, with a thickness of 1µm, with different hydrogen concentrations, prepared by hot wire deposition were crystallized by 514,5 nm cw Ar ion laser radiation, with a power density between 150 and 270 kW/cm2. The crystallization was continuously monitored by Raman spectroscopy for exposures up to hours. The analysis of the crystallization process using Johnson-Mehl phenomological equations showed an apparent crystallization energy of around 0.5 eV and low dimensional crystal growth. The mean value of the crystal size decreases with increasing irradiation energy and initial hydrogen content and varies between 3 and 6 nm.

RECRYSTALLIZATION OF AMORPHOUS Si BY LASER IRRADIATION(.MS Word)

Copyright © 2004  Department of Physics ! All Rights Reserved.