Semiconductor and Optical Materials Commons^™

Enhanced Light Extraction Efficiency From Gan Light Emitting Diodes Using Photonic Crystal Grating Structures, Simeon S. Trieu

Master's Theses

Gallium nitride (GaN) light emitting diodes (LED) embody a large field of research that aims to replace inefficient, conventional light sources with LEDs that have lower power, higher luminosity, and longer lifetime. This thesis presents an international collaboration effort between the State Key Laboratory for Mesoscopic Physics in Peking University (PKU) of Beijing, China and the Electrical Engineering Department of California Polytechnic State University, San Luis Obispo. Over the course of 2 years, Cal Poly’s side has simulated GaN LEDs within the pure blue wavelength spectrum (460nm), focusing specifically on the effects of reflection gratings, transmission gratings, top and bottom …

Optimization Of P3ht-Pcbm Polymer Solar Cells Through Device Simulation And Manufacturing, James Boom

Computer Engineering

Given a good model and implementation of that model, computer simulation can be used to reduce the time and material costs of research. To this end I worked with other students to manufacture, test and simulate the single layer P3HT-PCBM solar cell. Using the data collected from this project, future work can then be done with the project's simulator to further optimize these types of solar cell devices.

Production Of Multiwall Carbon Nanotuse For Alcohol Sensor Application., Ebtehal Saleh Alshaqaq

Student Works (2010-2019)

Multiwall carbon nanotube/polyethylene oxide (PEO), multiwall carbon nanoube/polyvinyl alcohol(PVA) and multiwall carbon nanotube/ polyvinyl alcohol(PVA)/zinc oxide(ZnO) have been tested as chemical sensors and detailed study on the effect of different gas concentration and material properties on gas sensitivity is presented. Initial composites were prepared by a simple solution casting and characterized by x-ray diffraction for ZnO, Fourier transform infra-red spectroscopy (FTIR) and scanning electron microscopy (SEM) to demonstrate crystallite size of ZnO, the morphology and surface area respectively. On the other hand, MWCNT/PEO , MWCNT/PVA , MWCNT/PVA/ZnO were prepared with different loading MWCNT and ZnO. The chemical sensing properties of …

Inductively Coupled Plasma Dry Etching Process On Planar Lightwave Circuit Fabrication., Chuah Khoon Seah

Student Works (2010-2019)

The main objective of this project is to master state-of-the-art techniques and knowledge in silica etching in order to achieve high quality waveguide circuit on Planar Lightwave Circuit devices. Another objective is to optimize the clean room research strength, surface characterization, microscopy techniques and similar semiconductor manufacturing processes.Initially, these processes were conducted with wet etching method that utilized diluted hydrofluoric acid (HF) and buffered oxide etch (BOE). Several problems arising such as mask peel-off, poor sidewall profile and defect waveguide channel during the pattern transfer process due to its’ isotropic nature. Alternatively, dry etching method was conducted via Inductively Coupled …

Excitation-Induced Germanium Quantum Dot Formation On Si (100)-(2×1), Ali Oguz Er, Hani E. Elsayed-Ali

Physics Faculty Publications

The effect of nanosecond pulsed laser excitation on the self-assembly of Ge quantum dots grown by pulsed laser deposition on Si (100)-(2×1) was studied. In situ reflection high-energy electron diffraction and ex situ atomic force microscopy were used to probe the quantum dot structure and morphology. At room temperature, applying the excitation laser decreased the surface roughness of the grown Ge film. With surface electronic excitation, crystalline Ge quantum dots were formed at 250 °C, a temperature too low for their formation without excitation. At a substrate temperature of 390 °C, electronic excitation during growth was found to improve the …

Giant Raman Enhancement On Nanoporous Gold Film By Conjugating With Nanoparticles For Single-Molecule Detection, Lihua Qian, Biswajit Das, Yan Li, Zhilin Yang

Electrical & Computer Engineering Faculty Research

Hot spots have the contradictively geometrical requirements for both the narrowest interstices to provide strong near-field coupling, and sufficient space to allow entrance of the analytes. Herein, a two-step method is employed to create hot spots within hybrid nanostructures, which consist of self-supported nanoporous gold films with the absorbed probes and subsequent nanoparticle conjugates without surface agents or mechanical motion. The molecules confined into 1 nm interstice exhibit 2.9 × 10⁷ times enhancement in Raman scattering compared to pure nanoporous gold. Giant enhancement primarily results from strong near-field coupling between nanopore and nanoparticle, which is theoretically confirmed by finite-difference …

Enhanced Visible Light Photoelectrochemical Performances With Nitrogen Doped Tio2 Nanowire Arrays, Xiao-Jun Lv, Yue-Ming Li, Hao Zhang, Da Chen, Jennifer Hensel, Jin Z Zhang, Jing-Hong Li

Journal of Electrochemistry

Self-organized anodic anatase TiO₂ nanowire arrays doped with nitrogen have been successfully fabri-cated and their photoelectrochemical(PEC) properties have been characterized and found to be substantially im-proved compared to undoped nanowires or commercial P25 nanoparticles.Photocurrent measured with monochro-matic incident light showed that the incident photon-to-current efficiency(IPCE,%) values of nanowire arrayelectrodes with or without N-doping were obviously higher than that of commercial P25 nanoparticle electrodes,and nitrogen-doped TiO₂ nanowire arrays(NTNA) had noticeable absorption in the visible region.The NTNAelectrodes showed the highest photocurrent density and power conversion efficiency under 100 mW/cm² visiblelight illumination.A maximumolphotoconversion efficiency of 0.52% was achieved for the …

Optimization Of Gan Laser Diodes Using 1d And 2d Optical Simulations, Sean Richard Keali'i Jobe

Master's Theses

This paper studies the optical properties of a GaN Laser Diode (LD). Through simulation, the GaN LD is optimized for the best optical confinement factor. It is found that there are optimal thicknesses of each layer in the diode that yield the highest optical confinement factor. There is a strong relationship between the optical confinement factor and lasing threshold—a higher optical confinement factor results in a lower lasing threshold. Increasing optical confinement improves lasing efficiency. Blue LDs are important to the future of lighting sources as they represent the final color in the RGB spectrum that does not have a …

Photoelectrochemical Properties Of Tio2 Nanoparticles, Jie Qu, Ying Li, Qi-Wei Jiang, Xue-Ping Gao

Journal of Electrochemistry

The protonated titanate nanoparticles were obtained at room temperature and subsequently calcined at different temperatures(300 ℃,400 ℃,500 ℃,600 ℃ and 700 ℃) in air.The obtained products were characterized by XRD,TEM and UV-Vis.It is found that the grain sizes of TiO₂ nanoparticles calcined at 300 ℃ were about 20 nm,and increased gradually with the temperature rise.Photoelectric performance was measured with I～V curve and electrochemical impedance spectroscopy(EIS).The TiO₂ nanoparticles obtained at 500 ℃ showed the best photoelectrochemical properties with a photovoltaic conversion efficiency of 6.39%,which is much higher than those at other temperatures.In addition,it is also demonstrated that the charge …

Model For Alumina Nanopore-Based Optical Filter, Nathan Lehman, Rama Venkat, Robert A. Schill

Electrical & Computer Engineering Faculty Research

Alumina nanopore structures find applications in magnetic sensors, optical filters, and various biological devices. In this work, we present a ray-optics model for the optical filter. We present a detailed simulation and a simplified analytical expression for the reflectance as a function of the alumina parameters such as pore diameter, pore density, alumina thickness, and a function of the wavelength and angle of incidence of the illuminating plane electromagnetic wave. The reflectance vs wavelength in the range of 400–800nm obtained from the simulation and the analytical expression are compared with that of the experiments for thin and thick alumina. All …

Study On The Texturization Of C-Si Wafers By Different Kinds Of Alkaline For Heterojunction Solar Cells, Yu-Hua Dou, Yu-Qin Zhou, Mei-Fang Zhu, Shuang Song, Feng-Zhen Liu, Jin-Long Liu, Zhan-Jun Zhang

Journal of Electrochemistry

The texturization of(100) crystalline silicon(c-Si) wafer was studied by field-emission scanning electron microscope using different kinds of etchant: sodium hydroxide,sodium carbonate and tribasic sodium phosphate.By optimizing the etching parameters,the lowest values of averaged reflectance(Rav) were obtained to be 9.70% for NaOH,9.76% for Na₂CO₃ and 8.63% for Na₃PO₄·12H₂O,which is comparable to that of the wafer with textured surface covered with an anti-reflection coating of either silicon nitride or thermally grown silicon dioxide.The relation of Rav and surface morphology of textured wafer was analyzed.Moreover,special emphasis was put on the role of isopropyl alcohol(IPA) …

The Effect Of Radiation On The Electrical Properties Of Aluminum Gallium Nitride/Gallium Nitride Heterostructures, John W. Mcclory

Theses and Dissertations

AlGaN/GaN Heterojunction Field Effect Transistors (HFETs) were irradiated at low temperature and the temperature dependent changes to drain current, gate current, capacitance, and transconductance were measured. The results were compared to the charge control model of the drain current and trap-assisted tunneling model of the gate current to determine the source of the radiation-induced changes. AlGaN/GaN HFETs demonstrated threshold voltage shifts and drain current changes after irradiation. After electron and neutron irradiation applied at ~80 K, measurement of the drain current at this temperature showed an increase that saturated after 10¹³ electrons/cm² or 10¹⁰ neutrons/cm² due …

Preparation And Photoelectrochemical Properties Of Fe-Doped Tio2 Nanotube Arrays, Jing Li, Lan Sun, Hui-Fang Zhuang, Cheng-Lin Wang, Rong-Gui Du, Chang-Jian Lin

Journal of Electrochemistry

The Fe-doped TiO₂ nanotube arrays were fabricated in Fe(NO₃)₃-HF mixing solutions by electrochemical anodic oxidation method,and characterized by FESEM,Raman,XPS and DRS.The effect of Fe concentratiions on photoelectrochemical property of the arrays was also investigated.The diameters and lengths of Fe-doped TiO₂ nanotube arrays were 50~90 nm and about 200 nm,respectively.Compared with the undoped TiO₂ nanotube arrays,the absorption edge of Fe-doped TiO₂ nanotube arrays appeared red shifting.The more Fe content,the larger red shifting,in addition,the photocurrent of Fe-doped TiO₂ nanotube arrays increased obviously.

An Ultrahigh Vacuum Complementary Metal Oxide Silicon Compatible Nonlithographic System To Fabricate Nanoparticle-Based Devices, Arghya Banerjee, Biswajit Das

Electrical & Computer Engineering Faculty Research

Nanoparticles of metals and semiconductors are promising for the implementation of a variety of photonic and electronic devices with superior performances and new functionalities. However, their successful implementation has been limited due to the lack of appropriate fabrication processes that are suitable for volume manufacturing. The current techniques for the fabrication of nanoparticles either are solution based, thus requiring complex surface passivation, or have severe constraints over the choice of particle size and material. We have developed an ultrahigh vacuum system for the implementation of a complex nanosystem that is flexible and compatible with the silicon integrated circuit process, thus …

Activation Energy Of Surface Diffusion And Terrace Width Dynamics During The Growth Of In (4×3) On Si (100) - (2×1) By Femtosecond Pulsed Laser Deposition, M. A. Hafez, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

The nucleation and growth of indium on a vicinal Si (100) - (2×1) surface at high temperature by femtosecond pulsed laser deposition was investigated by in situ reflection high energy electron diffraction (RHEED). RHEED intensity relaxation was observed for the first ∼2 ML during the growth of In (4×3) by step flow. From the temperature dependence of the rate of relaxation, an activation energy of 1.4±0.2 eV of surface diffusion was determined. The results indicate that indium small clusters diffused to terrace step edges with a diffusion frequency constant of (1.0±0.1) × 10¹¹ s^-1. The RHEED specular …

Nonthermal Laser-Induced Formation Of Crystalline Ge Quantum Dots On Si(100), M. S. Hegazy, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

The effects of laser-induced electronic excitations on the self-assembly of Ge quantum dots on Si (100) - (2×1) grown by pulsed laser deposition are studied. Electronic excitations due to laser irradiation of the Si substrate and the Ge film during growth are shown to decrease the roughness of films grown at a substrate temperature of ∼120 °C. At this temperature, the grown films are nonepitaxial. Electronic excitation results in the formation of an epitaxial wetting layer and crystalline Ge quantum dots at ∼260 °C, a temperature at which no crystalline quantum dots form without excitation under the same deposition conditions. …

Band Gap Engineering Of Two Dimensional Silicon Photonic Crystals By Oxidation And Oxide Etching, Makhin Thitsa

Electrical & Computer Engineering Theses & Dissertations

In this thesis a thorough analysis is presented on the effects of oxidation and oxide etching on the band structure of two dimensional silicon photonic crystals (2 D Si PC's). By using the plane wave expansion method (PWM), two structures of triangular lattice, namely, air cylinders embedded in a silicon background and silicon cylinders embedded in an air background are modeled. The thesis focuses on triangular lattice arrangement because for certain parameter values such a lattice can give rise to absolute band gap, which prohibits the propagation of either transverse electric (TE) or transverse magnetic (TM) polarizations.

During oxidation three …

Formation Of In- (2×1) And In Islands On Si (100) - (2×1) By Femtosecond Pulsed Laser Deposition, M. A. Hafez, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

The growth of indium on a vicinal Si (100) - (2×1) surface at room temperature by femtosecond pulsed laser deposition (fsPLD) was investigated by in situ reflection high-energy electron diffraction (RHEED). Recovery of the RHEED intensity was observed between laser pulses and when the growth was terminated. The surface diffusion coefficient of deposited In on initial two-dimensional (2D) In- (2×1) layer was determined. As growth proceeds, three-dimensional In islands grew on the 2D In- (2×1) layer. The RHEED specular profile was analyzed during film growth, while the grown In islands were examined by ex situ atomic force microscopy. The full …

Analysis Of Photoconductive Properties In Ge2Sb2Te5 (Gst) Chalcogenide Films For Applications In Novel Electronics, John R. V. Chezem

Theses and Dissertations

This thesis investigated the thermal phase-change properties in Ge₂Sb₂Te₅ (GST) chalcogenide-based films and determined the feasibility of coupling the GST with photosensitive DNA material for novel optical device applications. Modeling and testing of GST were researched with the approach that GST would react as a resistive mechanism through thermal manipulation. A test structure was fabricated with a 2-micronmeter MEMS fabrication process. GST material was deposited (by RF sputtering) on the surface of the test structures. The GST was analyzed primarily in the amorphous to crystalline transition states due to more distinct changes in the resistance …

Special Photoelectrochemical Response Of Nano-Crystalline Tio2 Electrode, Bi-Bo Lan, Jian-Zhang Zhou, Yan-Yan Xi, Hong-Xiang Chen, Guang-Hua Yao, Zhong-Hua Lin

Journal of Electrochemistry

The nano-crystalline TiO₂ electrodes were prepared by spread method,electrodeposition and sol-gel method.The experimental results show that the nano-crystalline TiO₂ electrodes have special photoelectrochemical response-the photocrrent-potential curves appear peaks.The special photoelectrochemical behaviors of nano-(crystalline) TiO₂  electrodes are ascribed to nano-structure as well as special light induced redox reaction mechanism of nano-crystalline semiconductor electrodes.

Melting And Solidification Study Of As-Deposited And Recrystallized Bi Thin Films, M. K. Zayed, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

Melting and solidification of as-deposited and recrystallized Bi crystallites, deposited on highly oriented 002-graphite at 423 K, were studied using reflection high-energy electron diffraction (RHEED). Films with mean thickness between 1.5 and 33 ML (monolayers) were studied. Ex situ atomic force microscopy was used to study the morphology and the size distribution of the formed nanocrystals. The as-deposited films grew in the form of three-dimensional crystallites with different shapes and sizes, while those recrystallized from the melt were formed in nearly similar shapes but different sizes. The change in the RHEED pattern with temperature was used to probe the melting …

Combinatorial Study Of Ni-Ti-Pt Ternary Metal Gate Electrodes On Hfo2 For The Advanced Gate Stack, K.-S. Chang, M. L. Green, J. Suehle, E. M. Vogel, H. Xiong, Jason R. Hattrick-Simpers, I. Takeuchi, O. Famodu, K. Ohmori, P. Ahmet, T. Chikyow, P. Majhi, B.-H. Lee, M. Gardner

Faculty Publications

The authors have fabricated combinatorial Ni–Ti–Pt ternary metal gate thin film libraries on HfO₂ using magnetron co-sputtering to investigate flatband voltage shift (ΔV_fb) , work function (Φ_m) , and leakage current density (J_L) variations. A more negative ΔV_fb is observed close to the Ti-rich corner than at the Ni- and Pt-rich corners, implying smaller Φ_m near the Ti-rich corners and higher Φ_m near the Ni- and Pt-rich corners. In addition, measured J_L values can be explained consistently with the observed Φ_m variations. Combinatorial methodologies prove to be useful …

Growth Of Ge Quantum Dots On Si(100)-(2×1) By Pulsed Laser Deposition, M. S. Hegazy, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

Self-assembled germanium quantum dots (QDs) were grown on Si(100)-(2×1) by pulsed laser deposition. In situ reflection-high energy electron diffraction (RHEED) and postdeposition atomic force microscopy are used to study the growth of the QDs. Several films of different thicknesses were grown at a substrate temperature of 400 °C using a Q-switched Nd:yttrium aluminum garnet laser (λ= 1064 nm, 40 ns pulse width, 23 J/cm ² fluence, and 10 Hz repetition rate). At low film thicknesses, hut clusters that are faceted by different planes, depending on their height, are observed after the completion of the wetting layer. With increasing film thickness, …

Tunable Multiferroic Properties In Nanocomposite Pbtio3-Cofe2O4 Epitaxial Thin Films, M. Murakami, K.-S. Chang, M. A. Aronova, C.-L. Lin, Ming H. Yu, Jason R. Hattrick-Simpers, M. Wuttig, I. Takeuchi, C. Gao, B. Hu, S. E. Lofland, L. A. Knauss, L. A. Bendersky

Faculty Publications

We report on the synthesis of PbTiO₃–CoFe₂O₄ multiferroic nanocomposites and continuous tuning of their ferroelectric and magnetic properties as a function of the average composition on thin-film composition spreads. The highest dielectric constant and nonlinear dielectric signal was observed at (PbTiO₃)₈₅–(CoFe₂O₄)₁₅, where robust magnetism was also observed. Transmission electron microscopy revealed a pancake-shaped epitaxial nanostructure of PbTiO₃ on the order of 30 nm embedded in the matrix of CoFe₂O₄ at this composition. Composition dependent ferroics properties observed here indicate that there …

Self-Assembly Of Ge Quantum Dots On Si(100)- 2×1 By Pulsed Laser Deposition, M. S. Hegazy, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

Self-assembled Ge quantum dots are grown on Si(100)- 2×1 by pulsed laser deposition. The growth is studied by in situ reflection high-energy electron diffraction and postdeposition atomic force microscopy. After the completion of the wetting layer, transient hut clusters, faceted by different planes, are observed. When the height of these clusters exceeded a certain value, the facets developed into {305} planes. Some of these huts become {305}-faceted pyramids as the film mean thickness was increased. With further thickness increase, dome clusters developed on the expense of these pyramids. © 2005 American Institute of Physics. [DOI: 10.1063/1.1949285]

Preparation, Characterization And Photoelectrochemical Activities Of Cu-Tio2/Ito Films, Dong Shu, Chun He, Han-Xia Zhang, Ya Xiong

Journal of Electrochemistry

Cu-TiO₂/ITO films were prepared by direct photo-reduction deposition of Cu²⁺ on TiO₂/ITO films. The nanocomposite films were characterized by UV-vis diffuse reflectance spectra (DRS), XRD spectra, Scanning Electron Microscope (SEM) technology, and photovoltage measurement. The feasibility of improving the photocatalytic activity of TiO₂ film by combining the modification of Cu nanoparticles with the application of anodic bias was investigated. The experimental results showed that the deposited Cu has an apparent enhancement effect with respect to suppressing the recombination between the photogenerated charge carriers and enhancing the photocatalytic oxidation of formic acid. The combination could …

Study Of Transport Properties Of Inas Using Monte Carlo Simulation, Satyanadh Gundimada

Electrical & Computer Engineering Theses & Dissertations

The present research is aimed at ascertaining the usefulness of InAs semiconductor material for single photon avalanche photo detectors operating in the Geiger mode at 2 μm wavelengths. InAs is considered as the material suitable for the purpose because of its less bandgap and lower effective mass of the electrons when compared to other semiconductor materials presently in use. Hence, theoretically transient transport properties of bulk InAs are superior and the velocity overshoot phenomena stronger. InAs is a relatively less explored material when compared to other materials like GaAs. The choice of the material is justified with thorough exploration of …

Photoelectrochemistry Of La3+ Doped Semiconductor Porous Films Sensitized By Ru(Bpy)2(Ncs)2 Dye, Li Zhang, Yan-Jie Ren, Sheng-Min Cai

Journal of Electrochemistry

The La³⁺-doped TiO₂ nanoparticles were prepared with hydrothermal method.The photoelectrochemical properties of La³⁺-doped TiO₂ nanoporous-film electrode sensitized by Ru(bpy)₂(NCS)₂ were studied. The conversion efficiency of light to electricity and the energy conversion efficiencies were ineased with the depth of La³⁺-doped TiO₂ nanoporous-film electrode.

Oxidation-Induced Stacking Fault In (100) And (111) Silicon Wafers, Mei Keat Liang

Student Works (2000-2009)

Oxidation-induced stacking fault (OISF) dimension and density change on (100) and (111) wafers, as a result of repeated preferential etching were studied using AFM. optical microscope and angular polishing techniques. Density on (100) and (111) wafers is independent of surface removal up to 3.0µm. This indicates the single layer nature of OISF formed from the sand blasted wafer. Besides having higher density, OISFs from (100) wafer were longer than OISF from (111) wafer. OISF width increases linearly with surface removal however the length does not change significantly with surface removal. ln the OISF normal depth studies using angular polishing technique, …

The Effect Of Preparation Condition On The Photoelectrochemical Performance Of Both The Pani Film And Tio2-Pani Composite Film On Au, Huai-Guo Huang, Hong-Ping Zhang, Zhi-Xin Zheng, Yan-Yan Xi, Ling-Ling Wu, Zhong-Hua Lin

Journal of Electrochemistry

Both the PANI (polyaniline) film and TiO₂-PANI composite film on the PATP(paminothiophenol)/Au substrate were obtained under different preparation condition by electrochemical methods, and their photoelectrochemical performances were alo studied. The resultsshowed that the photoelectrochemical performances of the films depend deeply on the comditionsof preparation. The self-assembling of PATP favors the adhesion of PANl. The partially-oxidizedPANI has a greater photoelectrochemical response than that of the reduced PANI and oxidized PANl. There is an optimum of film thickness for the photoelectrochemical performance of PANI film. Heat treating is in favor of the photoelectrochemical performance of TiO₂, but decreases …