Electronic Devices and Semiconductor Manufacturing Commons^™

Nano-Patterned Si Structures For Optical Filters And Electro-Mechanical Relays: Fabrication, Characterization, Prospects, And Limitations, Md Ataul Mamun

Theses and Dissertations

Nanofabrication technology, especially nanopatterning, is a rapidly advancing field that has already resulted in creating novel devices and holds promise for producing even more with unmatched performance. These techniques also allow us to gain insight into physical phenomena at the micro- and nanoscale. The ultimate performance of nanofabricated devices and their compatibility with existing Si-based CMOS technology hinge upon the careful selection of materials and precise design, coordinated with meticulous pattern transfer. In this work, we applied nanopatterning techniques on silicon to create optical filters for the shortwave infrared (SWIR) region and nanoelectromechanical system (NEMS) relay-based logic gates. Additionally, these …

Photoluminescence Of Beryllium-Related Defects In Gallium Nitride, Mykhailo Vorobiov, Mykhailo Vorobiov

Theses and Dissertations

This study explores the potential of beryllium (Be) as an alternative dopant to magnesium (Mg) for achieving higher hole concentrations in gallium nitride (GaN). Despite Mg prominence as an acceptor in optoelectronic and high-power devices, its deep acceptor level at 0.22 eV above the valence band limits its effectiveness. By examining Be, this research aims to pave the way to overcoming these limitations and extend the findings to aluminum nitride and aluminum gallium nitride (AlGaN) alloy. Key contributions of this work include. i)Identification of three Be-related luminescence bands in GaN through photoluminescence spectroscopy, improving the understanding needed for further material …

Low Insertion-Loss Nanophotonic Modulators Through Epsilon-Near-Zero Material-Based Plasmon-Assisted Approach For Integrated Photonics, Mohammad Ariful Hoque Sojib

Theses and Dissertations

Electro-optic/absorption Modulators (EOM/EAMs) encode high-frequency electrical signals into optical signals. With the requirement of large packing density, device miniaturization is possible by confining light in a sub-wavelength dimension by utilizing the plasmonic phenomenon. In plasmon, energy gets transferred from light to the form of oscillation of free electrons on a surface of a metal at an interface between the metal and a dielectric. Plasmonic provides increased light-matter interaction (LMI) and thus making the light more sensitive to local refractive index change. Plasmonic-based integrated nanophotonic modulators, despite their promising features, have one key limiting factor of large Insertion Loss (IL) which …

Perovskite Thin Films Annealed In Supercritical Fluids For Efficient Solar Cells, Gilbert Annohene

Theses and Dissertations

In the field of photovoltaics, scientists and researchers are working fervently to produce a combination of efficient, stable, low cost and scalable devices. Methylammonium lead trihalide perovskite has attracted intense interest due to its high photovoltaic performance, low cost, and ease of manufacture. Their high absorption coefficient, tunable bandgap, low-temperature processing, and abundant elemental constituent provide innumerable advantages over other thin film absorber materials. Since the perovskite film is the most important in the device, morphology, crystallization, compositional and interface engineering have been explored to boost its performance and stability. High temperatures necessary for crystallization of organic-inorganic hybrid perovskite films …

On-Demand Electrically Induced Decomposition Of Thin-Film Nitrocellulose Membranes For Wearable Or Implantable Biosensor Systems, Benjamin M. Horstmann

Theses and Dissertations

Implantable or subcutaneous biosensors used for continuous health monitoring have a limited functional lifetime requiring frequent replacement and therefore may be highly discomforting to the patient and become costly. One possible solution to this problem is use of biosensor arrays where each individual reserve sensor can be activated on-demand when the previous one becomes inoperative due to biofouling or enzyme degradation. Each reserve biosensor in the array is housed in an individual Polydimethylsiloxane (PDMS) well and is protected from exposure to bodily fluids such as interstitial fluid ( ISF) by a thin-film nitrocellulose membrane. Controlled activation is achieved by decomposing …

Electric Field Control Of Fixed Magnetic Skyrmions For Energy Efficient Nanomagnetic Memory, Dhritiman Bhattacharya

Theses and Dissertations

To meet the ever-growing demand of faster and smaller computers, increasing number of transistors are needed in the same chip area. Unfortunately, Silicon based transistors have almost reached their miniaturization limits mainly due to excessive heat generation. Nanomagnetic devices are one of the most promising alternatives of CMOS. In nanomagnetic devices, electron spin, instead of charge, is the information carrier. Hence, these devices are non-volatile: information can be stored in these devices without needing any external power which could enable computing architectures beyond traditional von-Neumann computing. Additionally, these devices are also expected to be more energy efficient than CMOS devices …

Resonant Acoustic Wave Assisted Spin-Transfer-Torque Switching Of Nanomagnets, Austin R. Roe

Theses and Dissertations

We studied the possibility of achieving an order of magnitude reduction in the energy dissipation needed to write bits in perpendicular magnetic tunnel junctions (p-MTJs) by simulating the magnetization dynamics under a combination of resonant surface acoustic waves (r-SAW) and spin-transfer-torque (STT). The magnetization dynamics were simulated using the Landau-Lifshitz-Gilbert equation under macrospin assumption with the inclusion of thermal noise. We studied such r-SAW assisted STT switching of nanomagnets for both in-plane elliptical and circular perpendicular magnetic anisotropy (PMA) nanomagnets and show that while thermal noise affects switching probability in in-plane nanomagnets, the PMA nanomagnets are relatively robust to the …

Straintronic Nanomagnetic Devices For Non-Boolean Computing, Md Ahsanul Abeed

Theses and Dissertations

Nanomagnetic devices have been projected as an alternative to transistor-based switching devices due to their non-volatility and potentially superior energy-efficiency. The energy efficiency is enhanced by the use of straintronics which involves the application of a voltage to a piezoelectric layer to generate a strain which is ultimately transferred to an elastically coupled magnetostrictive nanomaget, causing magnetization rotation. The low energy dissipation and non-volatility characteristics make straintronic nanomagnets very attractive for both Boolean and non-Boolean computing applications. There was relatively little research on straintronic switching in devices built with real nanomagnets that invariably have defects and imperfections, or their adaptation …

Energy Efficient Spintronic Device For Neuromorphic Computation, Md Ali Azam

Theses and Dissertations

Future computing will require significant development in new computing device paradigms. This is motivated by CMOS devices reaching their technological limits, the need for non-Von Neumann architectures as well as the energy constraints of wearable technologies and embedded processors. The first device proposal, an energy-efficient voltage-controlled domain wall device for implementing an artificial neuron and synapse is analyzed using micromagnetic modeling. By controlling the domain wall motion utilizing spin transfer or spin orbit torques in association with voltage generated strain control of perpendicular magnetic anisotropy in the presence of Dzyaloshinskii-Moriya interaction (DMI), different positions of the domain wall are realized …

Fabrication And Simulation Of Nanomagnetic Devices For Information Processing, Justine L. Drobitch

Theses and Dissertations

Nanomagnetic devices are highly energy efficient and non-volatile. Because of these two attributes, they are potential replacements to many currently used information processing technologies, and they have already been implemented in many different applications. This dissertation covers a study of nanomagnetic devices and their applications in various technologies for information processing – from simulating and analyzing the mechanisms behind the operation of the devices, to experimental investigations encompassing magnetic film growth for device components to nanomagnetic device fabrication and measurement of their performance.

Theoretical sections of this dissertation include simulation-based modeling of perpendicular magnetic anisotropy magnetic tunnel junctions (p-MTJ) and …

Low-Temperature Fabrication Process For Integrated High-Aspect Ratio Metal Oxide Nanostructure Semiconductor Gas Sensors, William Paul Clavijo

Theses and Dissertations

This work presents a new low-temperature fabrication process of metal oxide nanostructures that allows high-aspect ratio zinc oxide (ZnO) and titanium dioxide (TiO₂) nanowires and nanotubes to be readily integrated with microelectronic devices for sensor applications. This process relies on a new method of forming a close-packed array of self-assembled high-aspect-ratio nanopores in an anodized aluminum oxide (AAO) template in a thin (2.5 µm) aluminum film deposited on a silicon and lithium niobate substrate (LiNbO₃). This technique is in sharp contrast to traditional free-standing thick film methods and the use of an integrated thin aluminum film …

Growth Of Zn-Polar Bemgzno/Zno Heterostructure With Two Dimensional Electron Gas (2deg) And Fabrication Of Silver Schottky Diode On Bemgzno/Zno Heterostructure., Md Barkat Ullah

Theses and Dissertations

Title of dissertation: GROWTH OF Zn POLAR BeMgZnO/ZnO HETEROSTRUCTURE WITH TWO DIMENSIONAL ELECTRON GAS (2DEG) AND FABRICATION OF SILVER SCHOTTKY DIODE ON BeMgZnO/ZnO HETEROSTRUCTURE

By Md Barkat Ullah, Ph.D

A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical and Computer Engineering at Virginia Commonwealth University.

Virginia Commonwealth University,2017

Major Director: Dr. Hadis Morkoç, Professor, Electrical and Computer Engineering

This thesis focuses on growth of Zn polar BeMgZnO/ZnO heterostructure on GaN/sapphire template with two dimensional electron gas (2DEG) for the application of UV photodetector/emitter and high speed electronics. The motivation of using …

Optical Spectroscopy Of Wide Bandgap Semiconductor Heterostructures And Group-Iv Alloy Quantum Dots, Tanner A. Nakagawara

Theses and Dissertations

Efficient and robust blue InGaN multiple quantum well (MQW) light emitters have become ubiquitous; however, they still have unattained theoretical potential. It is widely accepted that “localization” of carriers due to indium fluctuations theoretically enhance their efficiency by moderating defect-associated nonradiative recombination. To help develop a complete understanding of localization effects on carrier dynamics, this thesis explores degree of localization in InGaN MQWs and its dependence on well thickness and number of wells, through temperature and power dependent photoluminescence measurements. Additionally, silicon-compatible, nontoxic, colloidally synthesizable 2-5 nm Ge_1-xSn_x alloy quantum-dots (QDs) are explored for potential visible to …

Hybrid Straintronics-Spintronics: Energy-Efficient Non-Volatile Devices For Boolean And Non-Boolean Computation, Ayan K. Biswas

Theses and Dissertations

Research in future generation computing is focused on reducing energy dissipation while maintaining the switching speed in a binary operation to continue the current trend of increasing transistor-density according to Moore’s law. Unlike charge-based CMOS technology, spin-based nanomagnetic technology, based on switching bistable magnetization of single domain shape-anisotropic nanomagnets, has the potential to achieve ultralow energy dissipation due to the fact that no charge motion is directly involved in switching. However, switching of magnetization has not been any less dissipative than switching transistors because most magnet switching schemes involve generating a current to produce a magnetic field, or spin transfer …

Electric Field Controlled Strain Induced Switching Of Magnetization Of Galfenol Nanomagnets In Magneto-Electrically Coupled Multiferroic Stack, Hasnain Ahmad

Theses and Dissertations

The ability to control the bi-stable magnetization states of shape anisotropic single domain nanomagnets has enormous potential for spawning non-volatile and energy-efficient computing and signal processing systems. One of the most energy efficient switching methods is to adopt a system of a 2-phase multiferroic nanomagnet, where a voltage applied on the piezoelectric layer generates a strain in it and the strain is elastically transferred to the magnetostrictive nanomagnet which rotates the magnetization states of the nanomagnet at room temperature via the converse magnet-electric effect. Recently, it has been demonstrated that the magnetization of a Co nanomagnet can be switched between …

Ultra–Low Power Straintronic Nanomagnetic Computing With Saw Waves: An Experimental Study Of Saw Induced Magnetization Switching And Properties Of Magnetic Nanostructures, Vimal G. Sampath

Theses and Dissertations

A recent International Technology Roadmap for Semiconductors (ITRS) report (2.0, 2015 edition) has shown that Moore’s law is unlikely to hold beyond 2028. There is a need for alternate devices to replace CMOS based devices, if further miniaturization and high energy efficiency is desired. The goal of this dissertation is to experimentally demonstrate the feasibility of nanomagnetic memory and logic devices that can be clocked with acoustic waves in an extremely energy efficient manner. While clocking nanomagnetic logic by stressing the magnetostrictive layer of a multiferroic logic element with with an electric field applied across the piezoelectric layer is known …

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 …

Optical Investigations Of Ingan Heterostructures And Gesn Nanocrystals For Photonic And Phononic Applications: Light Emitting Diodes And Phonon Cavities, Shopan D. Hafiz

Theses and Dissertations

InGaN heterostructures are at the core of blue light emitting diodes (LEDs) which are the basic building blocks for energy efficient and environment friendly modern white light generating sources. Through quantum confinement and electronic band structure tuning on the opposite end of the spectrum, Ge_1−xSn_x alloys have recently attracted significant interest due to its potential role as a silicon compatible infra-red (IR) optical material for photodetectors and LEDs owing to transition to direct bandgap with increasing Sn. This thesis is dedicated to establishing an understanding of the optical processes and carrier dynamics in InGaN heterostructures for achieving …

Strain Controlled Ultra-Low-Energy Magnetic Tunneling Junction, Hasnain Ahmad, Supriyo Bandyopadhyay, Jayasimha Atulasimha

Graduate Research Posters

We are experimenting on designing a voltage-controlled ultra-low-energy Magnetic Tunneling Junction (MTJ) device using a soft single domain magnetostrictive layer (i.e. Galfenol: Fe_1-xGa_x , x = 20 At%) coupled to a piezoelectric layer (i.e. PMN-PT). Special metal pads have been designed using photolithography to generate stress in the PMN-PT layer by applying electric field. The patterns of different shape anisotropic nano-magnets are designed using e-beam lithography and we have successfully fabricate FeGa nanomagnets with only 12 to 13 nanometer thickness by sputter deposition. These nanomagnets have been characterized by magnetic force microscopy for observing their switching capabilities. …

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.

Electron – Phonon Interaction In Multiple Channel Gan Based Hfets: Heat Management Optimization, Romualdo A. Ferreyra

Theses and Dissertations

New power applications for managing increasingly higher power levels require that more heat be removed from the power transistor channel. Conventional treatments for heat dissipation do not take into account the conversion of excess electron energy into longitudinal optical (LO) phonons, whose associated heat is stored in the channel unless such LO phonons decay into longitudinal acoustic (LA) phonons via a Ridley path. A two dimensional electron gas (2DEG) density of ~5×10¹²cm^-2 in the channel results in a strong plasmon–LO phonon coupling (resonance) and a minimum LO phonon lifetime is experimentally observed, implying fast heat removal from …

Optical Characterization Of Ingan Heterostructures For Blue Light Emitters And Vertical Cavity Lasers: Efficiency And Recombination Dynamics, Serdal Okur

Theses and Dissertations

OPTICAL CHARACTERIZATION OF INGAN HETEROSTRUCTURES FOR BLUE LIGHT EMITTERS AND VERTICAL CAVITY LASERS: EFFICIENCY AND RECOMBINATION DYNAMICS

By Serdal Okur, Ph.D.

A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Virginia Commonwealth University.

Virginia Commonwealth University, 2014.

Major Director: Ümit Özgür, Associate Professor, Electrical and Computer Engineering

This thesis explores radiative efficiencies and recombination dynamics in InGaN-based heterostructures and their applications as active regions in blue light emitters and particularly vertical cavities. The investigations focus on understanding the mechanism of efficiency loss at high injection as well as developing designs to mitigate …

Quantum Efficiency Enhancement For Gan Based Light-Emitting Diodes And Vertical Cavity Surface-Emitting Lasers, Fan Zhang

Theses and Dissertations

This thesis explores the improvement of quantum efficiencies for InGaN/GaN heterostructures and their applications in light-emitting diodes (LEDs) and vertical cavity surface-emitting lasers (VCSELs). Different growth approaches and structural designs were investigated to identify and address the major factors limiting the efficiency. (1) Hot electron overflow and asymmetrical electron/hole injection were found to be the dominant reasons for efficiency degradation in nitride LEDs at high injection; (2) delta p-doped InGaN quantum barriers were employed to improve hole concentration inside the active region and therefore improve hole injection without sacrificing the layer quality; (3) InGaN active regions based on InGaN multiple …

Extending Device Performance In Photonic Devices Using Piezoelectric Properties, Gregory Edward Triplett

Electrical and Computer Engineering Publications

This study focuses on the influence of epi-layer strain and piezoelectric effects in asymmetric GaInAs/GaAlAs action regions that potentially lead to intra-cavity frequency mixing. The theoretical limits for conduction and valence band offsets in lattice-matched semiconductor structures have resulted in the deployment of non-traditional approaches such as strain compensation to extend wavelength in intersubband devices, where strain limits are related to misfit dislocation generation. Strain and piezoelectric effects have been studied and verified using select photonic device designs. Metrics under this effort also included dipole strength, oscillator strength, and offset of energy transitions, which are strongly correlated with induced piezoelectric …

Pseudomorphic Growth Of Inas On Misoriented Gaas For Extending Quantum Cascade Laser Wavelength, Gregory Edward Triplett, Charles Meyer, Emily Cheng, Justin Grayer, David Mueller, Denzil Roberts, Samuel Graham

Electrical and Computer Engineering Publications

The authors have studied the impact of epilayer strain on the deposition of InAs/GaAs on (100) and (111)B with 2 degrees offset toward 2-1-1 surfaces. Consequences of a 7% lattice mismatch between these orientations in the form of three-dimensional growth are less apparent for (111)B with 2 degrees offset toward 2-1-1 surfaces compared to (100). By exploring a range of molecular beam epitaxy process parameters for InAs/GaAs growth and utilizing scanning electron microscopy, atomic force microscopy, and Raman spectroscopy to evaluate the quality of these strained layers, the authors develop empirical models that describe the influence of the process conditions …

Charge Storage Characteristics Of Ultra-Small Pt Nanoparticle Embedded Gaas Based Non-Volatile Memory, Reginald Jeff, M Yun, B Ramalingam, B Lee, V Misra, Gregory Edward Triplett, Shubhra Gangopadhyay

Electrical and Computer Engineering Publications

Charge storage characteristics of ultra-small Pt nanoparticle embedded devices were characterized by capacitance-voltage measurements. A unique tilt target sputtering configuration was employed to produce highly homogenous nanoparticle arrays. Pt nanoparticle devices with sizes ranging from ∼0.7 to 1.34 nm and particle densities of ∼3.3–5.9 × 1012 cm−2 were embedded between atomic layer deposited and e-beam evaporated tunneling and blocking Al2O3 layers. These GaAs-based non-volatile memory devices demonstrate maximum memory windows equivalent to 6.5 V. Retention characteristics show that over 80% charged electrons were retained after 105 s, which is promising for device applications.

Reduced Auger Recombination In Mid-Infrared Semiconductor Lasers, Robert Bedford, Gregory Edward Triplett, David H. Tomich, Stephan W. Koch, Jerome Moloney, Jorg Hader

Electrical and Computer Engineering Publications

A quantum-design approach to reduce the Auger losses in two micron InGaSb type-I quantum well edge-emitting lasers is reported. Experimentally realized structures show a 3X reduction in the threshold, which results in 4.6 lower Auger current loss at room temperature. This is equivalent to a carrier lifetime improvement of 5.7 and represents about a 19-fold reduction in the equivalent “Auger coefficient.”