Engineering Physics Commons^™

Beyond Conventional C-Plane Gan-Based Light Emitting Diodes: A Systematic Exploration Of Leds On Semi-Polar Orientations, Morteza Monavarian

Theses and Dissertations

Despite enormous efforts and investments, the efficiency of InGaN-based green and yellow-green light emitters remains relatively low, and that limits progress in developing full color display, laser diodes, and bright light sources for general lighting. The low efficiency of light emitting devices in the green-to-yellow spectral range, also known as the “Green Gap”, is considered a global concern in the LED industry. The polar c-plane orientation of GaN, which is the mainstay in the LED industry, suffers from polarization-induced separation of electrons and hole wavefunctions (also known as the “quantum confined Stark effect”) and low indium incorporation efficiency that …

Spectrally-Resolved Imaging Of The Transverse Modes In Multimode Vcsels, Stephan A. Misak, Dan G. Dugmore, Kirsten A. Middleton, Evan R. Hale, Kelly R. Farner, Kent D. Choquette, Paul O. Leisher

Rose-Hulman Undergraduate Research Publications

Vertical-cavity surface-emitting lasers (VCSELs) enable a range of applications such as data transmission, trace sensing, atomic clocks, and optical mice. For many of these applications, the output power and beam quality are both critical (i.e. high output power with good beam quality is desired). Multi-mode VCSELs offer much higher power than single-mode devices, but this comes at the expense of lower beam quality. Directly observing the resolved mode structure of multi-mode VCSELs would enable engineers to better understand the underlying physics and help them to develop multi-mode devices with improved beam quality. In this work, a low-cost, high-resolution (<3 >pm) …

Reversible Mn Segregation At The Polar Surface Of Lithium Tetraborate, Christina L. Dugan, Robert L. Hengehold, Stephen R. Mchale, Juan A. Colon Santana, John W. Mcclory, Volodymyr T. Adamiv, Yaroslav V. Burak, Ya B. Losovyj, Peter A. Dowben

Faculty Publications

We find Mn surface segregation for single crystals of Mn doped Li₂B₄O₇, nominally Li_1.95Mn_0.05B₄O₇(001), but as the temperature increases, evidence of this Mn surface segregation diminishes significantly. At room temperature, the surface photovoltaic charging is significant for this pyroelectric material but is quenched at a temperature well below that seen for the undoped Li₂B₄O₇ samples. The suppression of surface charging in the region of 120 °C that accompanies the temperature of Mn dissolution in the bulk of Li₂B_{4 …}

Synthesis, Field Emission And Associated Degradation Mechanisms Of Tapered Zno Nanorods, Gregory M. Wrobel Mr.

Master's Theses

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Equation 2..... 4

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Equation 11..... 51

Synthesis, Field Emission and Associated Degradation Mechanisms of Tapered ZnO Nanorods

Gregory Michael Wrobel, M.S.

University of Connecticut, 2011

Modern development of field emitter arrays (FEA) has been made possible, partly thanks to the synthesis and development of one-dimensional (1D) nanostructures. High aspect ratio 1D nanostructures effectively amplify the electric field at the emitter tips, allowing electrons to be extracted at relatively low electric field. An inexpensive …

Time-Resolved Photoluminescence Of Inas/Gainsb Quantum Well Lasers, Michael R. Mckay

Theses and Dissertations

In the world of semiconductor photonic device fabrication, one important objective may be to extract as much light as possible from the device. In these devices, photons are created when electrons recombine with holes by transitioning from a high-energy state to a lower one. Unfortunately, electron-hole recombination does not always result in the formation of a photon. There are three basic types of recombination: the first results in the formation of a photon and is called radiative recombination; and the second and third, known as Shockley-Read-Hall and Auger recombination, result in the heating of the device and do not produce …

Experimental Investigation Of Nonlinear Dynamics In Single Mode Semiconductor Laser Diodes With Phase Conjugate Feedback, Gordon T. Hengst

Theses and Dissertations

The semiconductor laser diode offers a unique system to investigate nonlinear dynamics when optical feedback is applied. Although there is extensive research of laser diodes with optical feedback from normal dielectric mirrors, very little has been done experimentally to analyze the effects of degenerate phase conjugate feedback from a BaTiO₃ crystal. This research experimentally investigated the dynamics of a single-mode laser diode with weak phase conjugate feedback using both the self-pumped and double phase conjugate geometries. The experimental results validated a mathematical model which numerically evaluates the Lang-Kobayahsi coupled differential equations. The model simulated the nonlinear behavior of a …

Photoluminescence And Electroluminescence Of Erbium And Neodymium Implanted Semiconductors, James R. Hunter

Theses and Dissertations

Low temperature photoluminescence (PL) and electroluminescence (EL) measurements were used to study the excitation of erbium- and neodymium-implanted GaAs and Al_xGa_1-xAs (x=0. 1, 0.3) pn-junctions. The rare-earth (RE) emissions were investigated as a function of ion dose, aluminum mole fraction, laser excitation power, and applied forward bias voltage for the implanted samples. Low temperature PL was also measured from Er doped silicon grown by the metalorganic chemical vapor-phase deposition (MOCVD) method using various growth parameters.. The MOCVD-grown Si samples were studied as a function of metalorganic source temperature, silane (SiH₄) flow, growth time, and …

The Current Voltage Characteristics Of Electron Beam Controlled Thin Film Diamond Switches, Christopher Anthony Molina

Electrical & Computer Engineering Theses & Dissertations

The dark current of natural diamond thin films and the induced current due to electron-beam irradiation was measured up to a range of 7000Ncm'. The contact material was aluminum, annealed and unannealed. Switching experiments were performed with electron energies ranging from 70keV to 172keV. The switching results obtained are strongly dependent on the biasing polarity, incident electron energy, and whether the contact is blocking or Ohmic in nature. A simple model which takes traps into consideration allows us to explain the various switching responses. The range of electrons which define, in part, the switch mode was measured for one sample …

Light Injection From An Active Cladding To The Core Of A Fiber Optic Fluorosensor, Alvin Leon Bryant

Electrical & Computer Engineering Theses & Dissertations

A fluorosensor works on the basis of light injection from the clad into the core of an optical fiber. The sensitivity of such a sensor depends on the efficiency of light injection. Conditions necessary for a high injection efficiency are experimentally determined. The refractive index difference between the core and the clad,ⁿcore ^-nclad, must be maximized to achieve a high injection efficiency. Since an air clad has the least refractive index, a bare core fiber will have a maximum efficiency. Standard optical fibers used for communication employ a minimum value for ⁿcore ^-nclad, in order …

Processability Of Polythiophene Thin Films By Ultraviolet Photo Bleaching, Derek D. Fletcher

Theses and Dissertations

Materials possessing strong ��⁽³⁾ optical properties such as Polythiophene are sought for the production of optical switches. Polythiophene thin films produced by plasma enhanced CVD show a surface rms roughness of 10^-15 angstroms over single square micron areas which is acceptable for wave guiding in the near IR. This research investigates permanently changing the optical properties of such a thin film by exposure to UV radiation (254 nm, 35 mW/cm²), known as photo bleaching, in hope of creating a refractive index boundary for use in total internal reflection. After 60 minutes exposure the refractive index shows …

Fluorescent Lifetime Measurements Of Rare Earth Elements In Gallium Arsenide, Danny J. Topp

Theses and Dissertations

Lifetime measurements of the excited states of three GaAs semiconductors doped with the rare earth elements Erbium (ER), Praseodymium (Pr) , and Thulium (Tm) has been studied using a pulsed nitrogen laser and germanium detector. The measurements were made with an experimental set up with a system response time of 0.34 micro seconds. A 330 milliwatt nitrogen laser with a wavelength of 3370 angstrums was used to excite transitions of the rare earth elements.