Semiconductor and Optical Materials Commons^™

Development Of Low Temperature, Aqueous Synthesis Method Of Lead Sulfide Quantum Dots, Albert Nakao, Colin Yee

Materials Engineering

Quantum dots have become an active area of research in the past decade due to their unique properties. Quantum confinement effects allow for efficient spectral conversion and size tunable fluorescence and absorption peaks. Near infrared spectral converting lead sulfide quantum dots have potential applications in solar power, biological imaging and communications technology. However at Cal Poly, lead sulfide dots have not been synthesized. The quantum dot synthesis currently adapted at Cal Poly encompasses organometallic precursors at high reaction temperatures, producing cadmium selenium dots. The organometallic approach has been found to produce nanocrystals with high quality photoluminescence, but due to its …

Copper Doping Of Zno Crystals By Transmutation Of 64Zn To 65Cu: An Electron Paramagnetic Resonance And Gamma Spectroscopy Study, Matthew C. Recker, John W. Mcclory, Maurio S. Holston, Eric M. Golden, Nancy C. Giles, Larry E. Halliburton

Faculty Publications

Transmutation of ⁶⁴Zn to ⁶⁵Cu has been observed in a ZnO crystal irradiated with neutrons. The crystal was characterized with electron paramagnetic resonance (EPR) before and after the irradiation and with gamma spectroscopy after the irradiation. Major features in the gamma spectrum of the neutron-irradiated crystal included the primary 1115.5 keV gamma ray from the ⁶⁵Zn decay and the positron annihilation peak at 511 keV. Their presence confirmed the successful transmutation of ⁶⁴Zn nuclei to ⁶⁵Cu. Additional direct evidence for transmutation was obtained from the EPR of Cu²⁺ ions (where ⁶³Cu and ^{65 …}

Low Noise, High Detectivity Photodetectors Based On Organic Materials, Fawen Guo

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Organic photodetectors (OPDs) are potentially useful in many applications because of their light weight, flexibility and good form factors. Despite the high detectivities that have been frequently reported for OPDs recently, the application of these OPDs for weak light detection has been rarely demonstrated.

In this thesis, low noise, high gain photodetectors based on organic and ZnO nanoparticles were proposed and demonstrated for highly sensitive UV light detection. The nanocomposite photodetector works in a hybrid mode of photodiode and photoconductor with the transition controlled by the UV light illumination. The nanocomposite detector shows two orders of magnitude higher sensitivity than …

Design And Fabrication Of Electrostatically Actuated Serpentine-Hinged Nickel-Phosphorous Micromirror Devices, Nicholas A. Wiswell

Master's Theses

A process for micromachining of micro-mirror devices from silicon-on-insulator wafers was proposed and implemented. Test methods and force applicators for these devices were developed. Following successful fabrication of these devices, a novel process for fabrication of devices out of the plane of the silicon wafer was proposed, so that the devices could be actuated electrostatically. In particular, the process makes use of thick photoresist layers as a sacrificial mold into which an amorphous nickel-phosphorous alloy may be deposited. Ideal design of the electrostatically actuated micro-mirrors was investigated, and a final design was selected and modeled using FEA software, which found …

Fabrication And Characterization Of Edge-Emitting Semiconductor Lasers, Junyeob Song

Graduate Theses - Physics and Optical Engineering

The semiconductor laser was invented in 1962, and has recently become ubiquitous in modern life. This thesis focuses on the development of a semiconductor laser fabricating process which utilizes semiconductor manufacturing technology in a cleanroom environment including photolithography, etching, deposition, and bonding processes. A photomask for patterning is designed, recipes of photolithography process and etching process are developed with experiments. This work gives how to develop the process of fabrication and determine the parameters for each processes. A series of semiconductor laser devices are then fabricated using the developed process and characterization is performed to assess device performance with industrial …

Calculation And Experimental Verification Of Longitudinal Spatial Hole Burning In High-Power Semiconductor Lasers, Ting Hao

Graduate Theses - Physics and Optical Engineering

Longitudinal spatial hole burning (LSHB) is believed to be one of the limiting factors in scaling the output power of high-power semiconductor lasers. In this work, a self-consistent simulation of LSHB was performed to investigate the non-uniform longitudinal photon density distribution, carrier density distribution, and gain distribution in a high-power semiconductor laser. The calculation is based on a modification to the semiconductor laser rate equations and solved using a finite difference approach, with Newton’s method employed to numerically solve the differential equations. The impact of LSHB on output power was analyzed with different parameters, including injection current, cavity length, and …

A Comparison Of Pressure-Less Silver Sintering Materials With Conventional Electronic Die Attach Practices, Ross M. Liederbach

Electrical Engineering Undergraduate Honors Theses

This thesis contains information on an experiment which validates silver sintering paste manufacturer’s die attach processes and examines feasibility for use in commercial products. Four silver pastes were used in constructing die attach samples, which were then void and shear tested. The silver sintering materials that are investigated in this work are compared with manufacturer data and also with data from conventional attaches such as conductive epoxy and solder. In addition, materials demonstrating the highest shear strength were down-selected and processed to compare thermal characteristics with solder and conductive epoxy. Under theoretical analysis, the characteristics of silver provide the most …

The Synthesis And Characterization Of Copper Indium Sulfide And Cadmium Selenide Nanocrystals And Their Applications In Photodetectors, Zachary T. Bever

Electrical Engineering Undergraduate Honors Theses

Semiconductor nanocrystals are a topic of much interest in electrical engineering. Their use has been explored for many applications. This paper investigates the synthesis and characterization of CuInS2 and CdSe nanocrystals. As the nanocrystals were left in reaction for increasing amounts of time, the bandgap of the material decreased as the nanocrystal size increased due to the quantum confinement effect. The CdSe nanocrystals were then investigated in a photodetector application which achieved a detectivity on the order of 10^9 cmHz^(1/2)W^(-1).

Fabrication And Characterization Of Amorphous/Nanocrystalline Thin Film Composite, Benjamin Seth Newton

Graduate Theses and Dissertations

Combining the absorption abilities of amorphous silicon and the electron transport capabilities of crystalline silicon would be a great advantage to not only solar cells but other semiconductor devices. In this work composite films were created using molecular beam epitaxy and electron beam deposition interchangeably as a method to create metallic precursors. Aluminum induced crystallization techniques were used to convert an amorphous silicon film with a capping layer of aluminum nanodots into a film composed of a mixture of amorphous silicon and nanocrystalline silicon. This layer was grown into the amorphous layer by cannibalizing a portion of the amorphous silicon …

Design Of A Uv Curing Cartridge For 3d Inkjet Printing, Richard Wiswell

Thinking Matters Symposium Archive

In printing multi-layer electronic circuits, each layer must be formed as a continuous pattern in high resolution from ink jetted liquid droplets and be in precise alignment with the other layers, precluding substrate removal for UV curing. This research seeks to determine the optimal method for in-situ UV curing of the ink jetted material in a single pass. The inkjet replacement cartridge designed for this purpose was constructed of aluminum, fit into the printer head assembly in good alignment with the other ink cartridges, and contained a UV LED for in-situ curing and a cooling fan to maintain safe operating …

Hydrothermal Crystal Growth Of Lithium Tetraborate And Lithium ��-Metaborate, Jeffrey J. Graham

Theses and Dissertations

Growth of lithium tetraborate by the hydrothermal method was attempted in 10^-6 M LiOH, both by spontaneous nucleation and transport growth. Tetraborate grew out of the first spontaneous nucleation reaction, while the seed dissolved and lithium gamma-metaborate formed during the transport growth reactions. A species thermodynamic stability study showed gamma-metaborate formed exclusively from 350°C to 550°C, and Li₃B₅O₈(OH)₂ was observed at 250°C; tetraborate was not observed. A solubility study on lithium tetraborate did not achieve equilibrium conditions, but did demonstrate that gamma-metaborate is significantly more thermodynamically stable than tetraborate under the tested …

Investigation Of Degradation Effects Due To Gate Stress In Gan-On-Si High Electron Mobility Transistors Through Analysis Of Low Frequency Noise, Michael Curtis Meyer Masuda

Master's Theses

Gallium Nitride (GaN) high electron mobility transistors (HEMT) have superior performance characteristics compared to Silicon (Si) and Gallium Arsenide (GaAs) based transistors. GaN is a wide bandgap semiconductor which allows it to operate at higher breakdown voltages and power. Unlike traditional semiconductor devices, the GaN HEMT channel region is undoped and relies on the piezoelectric effect created at the GaN and Aluminum Gallium Nitride (AlGaN) heterojunction to create a conduction channel in the form of a quantum well known as the two dimensional electron gas (2DEG). Because the GaN HEMTs are undoped, these devices have higher electron mobility crucial for …

Triplet Ground State Of The Neutral Oxygen-Vacancy Donor In Rutile Tio2, A. T. Brant, Eric M. Golden, Nancy C. Giles, Shan Yang, M. A. R. Sarker, S. Watauchi, M. Nagao, I. Tanaka, D. A. Tryk, A. Manivannan, Larry E. Halliburton

Faculty Publications

Electron paramagnetic resonance (EPR) is used to investigate the triplet (S = 1) ground state of the neutral oxygen vacancy in bulk rutile TiO₂ crystals. This shallow donor consists of an oxygen vacancy with two nearest-neighbor, exchange-coupled ³⁺ ions located along the [001] direction and equidistant from the vacancy. The spins of the two trapped electrons, one at each ³⁺ ion, align parallel to give the S = 1 state. These neutral oxygen vacancies are formed near 25 K in as-grown oxidized TiO₂ crystals by illuminating with sub-band-gap 442 nm laser light. The angular dependence of the EPR …

A Systematic Study Of The Optical And Electrical Properties Of Ge1-YSnY And Ge1-X-YSiXSnY Semiconductor Alloys, Thomas R. Harris

Theses and Dissertations

In order to fully utilize newly developed Ge_1-ySn_y and Ge_1-x-ySi_xSn_y materials for new novel optoelectronic devices, the optical and electrical properties of these alloys were investigated using photoluminescence (PL) and Hall-effect measurements. Direct bandgap PL emission was observed from almost all the samples, making them very promising candidates for Si-based light emitting devices. T-dependent PL studies also indicate that the indirect-to-direct bandgap transition of Ge_1-ySn_y alloys might take place at a much lower Sn content than the theory predicts. T-dependent Hall-effect measurements showed both degenerate parallel conducting layers as …

Spectroscopy Studies Of Straincompensated Mid-Infrared Qcl Active Regions On Misoriented Substrates, Gregory Edward Triplett, Justin Grayer, Charles Meyer, Emily Cheng, Denzil Roberts

Electrical and Computer Engineering Publications

In this work, we perform spectroscopic studies of AlGaAs/InGaAs quantum cascade laser structures that demonstrate frequency mixing using strain-compensated active regions. Using a three-quantum well design based on diagonal transitions, we incorporate strain in the active region using single and double well configurations on various surface planes (100) and (111). We observe the influence of piezoelectric properties in molecular beam epitaxy grown structures, where the addition of indium in the GaAs matrix increases the band bending in between injector regions and demonstrates a strong dependence on process conditions that include sample preparation, deposition rates, mole fraction, and enhanced surface diffusion …

Orientation-Dependent Pseudomorphic Growth Of Inas For Use In Lattice-Mismatched Mid-Infrared Photonic Structures, Gregory Edward Triplett, Charles Meyer, Emily Cheng

Electrical and Computer Engineering Publications

In this study, InAs was deposited on GaAs (100) and GaAs (111)B 2 degrees towardssubstrates for the purpose of differentiating the InAs growth mode stemming from strain and then analyzed using in-situ reflection high energy electron diffraction, scanning electron microscopy, Raman spectroscopy, reflectance spectroscopy, and atomic force microscopy. The procession of InAs deposition throughout a range of deposition conditions results in assorted forms of strain relief revealing that, despite lattice mismatch for InAs on GaAs (approximately 7%), InAs does not necessarily result in typical quantum dot/wire formation on (111) surfaces, but instead proceeds two-dimensionally due primarily to the surface orientation.

Polarization Of Bi2te3 Thin Film In A Floating-Gate Capacitor Structure, Hui Yuan, Kai Zhang, Haitao Li, Hao Zhu, John E. Bonevich, Helmut Baumgart, Curt A. Richter, Qiliang Li

Electrical & Computer Engineering Faculty Publications

Metal-Oxide-Semiconductor (MOS) capacitors with Bi₂Te₃ thin film sandwiched and embedded inside the oxide layer have been fabricated and studied. The capacitors exhibit ferroelectric-like hysteresis which is a result of the robust, reversible polarization of the Bi₂Te₃ thin film while the gate voltage sweeps. The temperature-dependent capacitance measurement indicates that the activation energy is about 0.33 eV for separating the electron and hole pairs in the bulk of Bi₂Te₃, and driving them to either the top or bottom surface of the thin film. Because of the fast polarization speed, potentially excellent …

Stm Study Of Pulsed Laser Assisted Growth Of Ge Quantum Dot On Si(1 0 0)-(2 × 1), Ali Orguz Er, Hani E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

Ge quantum dot formation on Si(1 0 0)-(2 × 1) by nanosecond pulsed laser deposition under laser excitation was investigated. Scanning tunneling microscopy was used to probe the growth mode and morphology. Excitation was performed during deposition using laser energy density of 25-100 mJ/cm ². Faceted islands were achieved at a substrate temperature of ∼250 °C only when using laser excitation. The island morphology changes with increased laser excitation energy density although the faceting of the individual islands remains the same. The size of the major length of islands increases with the excitation laser energy density. A purely electronic …

Investigation Of The Effects Of Rapid Thermal Annealing On Mbe Grown Gaasbi/Gaas Heterostructures For Optoelectronic Devices, Perry C. Grant

Graduate Theses and Dissertations

High efficiency optoelectronic devices rely on high quality materials making up the device structure. The scope of this thesis investigates the effectiveness of rapid thermal annealing (RTA) at improving the material quality of GaAsBi/GaAs heterostructures. During the fabrication of a device, the contacts of the device had the rapid thermal annealing process accomplished to produce ohmic contacts and this research explored if this annealing treatment degraded the quantum wells that made up the active region of a device. To investigate these effects, a system to measure the photoluminescence of the material system was constructed utilizing Fourier Transform Infrared Spectroscopy. The …

Zinc Oxide Nanorod Based Ultraviolet Detectors With Wheatstone Bridge Design, Arun Vasudevan

Graduate Theses and Dissertations

This research work, for the first time, investigated metal semiconductor-metal (MSM) zine oxide (ZnO) nanorod based ultra-violet (UV) detectors having a Wheatstone bridge design with a high

responsivity at room temperature and above, as well as a responsivity that was largely independent of the change in ambient conditions. The ZnO nanorods which acted as the sensing element of the detector were grown by a chemical growth technique. Studies were conducted to determine the effects on ZnO nanorod properties by varying the concentration of the chemicals used for the rod growth. These studies showed how the rod diameter and the deposition …