Doctor of Philosophy in Materials Science and Engineering, Youngstown State University, 2024, Materials Science

Semiconductor materials have played a huge role in advancing today's technology through the electronic and photonic devices ushered in over the years. The advancement has been driven in part by society's growing need for electronic devices capable of handling higher power, higher temperature, and higher frequency. Current research efforts are expanding to ultra-wide bandgap semiconductors such as gallium oxide Ga2O3). The principal goal of this dissertation is to obtain high quality β-Ga2O3 films with controlled conductivity by magnetron sputtering deposition. The specific objectives are the following: To grow β-Ga2O3 films on sapphire substrates (section 5.2) and on native β-Ga2O3 by rf sputtering (section 5.3), to produce doped and undoped β-Ga2O3 films (Section 5.4). Additionally, to grow Lu2O3/ Ga2O3 and B2O3/Ga2O3 alloy films on (-2 0 1) UID or Sn-doped Ga2O3 and Al2O3 substrates to tune Ga2O3 original bandgap (Section 5.5). To obtain microstructural, morphological, compositional, and optical data from XRD, AFM, SEM, EDS, and UV-Vis characterization methods for all the experiments mentioned above. From this data, correlate the effects of the varying parameters for the optimization of the films, to use the developed films to fabricate Schottky barrier diodes and proceed with the electrical characterization of the fabricated devices (section 5.6).

Committee: Tom Oder PhD (Advisor); Clovis Linkous PhD (Committee Member); Constantin Solomon PhD (Committee Member); Michael Crescimanno PhD (Committee Member); Donald Priour PhD (Committee Member) Subjects: Electrical Engineering; Engineering; Experiments; Materials Science; Optics; Physics; Technology

Doctor of Philosophy, The Ohio State University, 2022, Chemistry

Numerous biological processes are carried out by the detection and interaction of small organic molecules, which assemble to form larger macrostructures. In Nature these processes are highly controlled, as small deformities can have deadly implications. Amino acids, peptides, nucleic acids, and proteins arrange with remarkable specificity into distinct structures that adapt, reorganize, and interact with their surroundings to enable the biological functions that characterize life. To truly duplicate the complexity, specificity, and operation of natural systems, however, it is essential to comprehend and design synthetic building blocks with controllable assembly properties and interactions. As an approach for creating responsive and adaptive materials, the self-assembly of organic peptide-based molecules into nanostructures was examined in the following studies. It is hoped that the advancements reported here in pH-controllable self-assembly, pathway control, and hierarchical structures can be further used to create nanomaterials for biomedical and optoelectronic applications.

Committee: Jon Parquette (Advisor) Subjects: Chemistry; Molecules; Morphology; Nanoscience; Nanotechnology; Organic Chemistry

Doctor of Philosophy, The Ohio State University, 2021, Electrical and Computer Engineering

This thesis presents the design and demonstration of high efficiency III-Nitride tunnel junctions for applications in tunnel junction-enabled III-nitride optoelectronic devices. The tunnel junctions are then utilized to study multi-junction cascaded LED structures for high output power applications. GaN light emitting diodes have been extremely successful in their applications for highly efficient solid-state lighting. There is still great interest in high power density III-Nitride visible emitters that could enable several new applications and reduce the cost associated with domestic, industrial, and automotive lighting. However, the drop in efficiency at high power/current density (known as the efficiency droop problem) makes it challenging to achieve high power density LEDs. The efficiency droop problem is one of the key unsolved issues for visible GaN LEDs, but multi-active region LEDs, consisting of identical active PN junctions and tunnel junctions (TJ), can provide an elegant solution to circumvent this challenge and enable high power emitters which operate at low current density, where efficiency droop is not as significant. First, a theoretical model was developed through TCAD simulations that offers a physics-based approach to understanding the key components of the design space which lead to a more efficient tunnel junction. Next, a sidewall activation process was optimized for buried magnesium-doped p-GaN layers yielding a significant reduction in tunnel junction-enabled LED forward voltage. This buried activation enabled the study of tunnel junctions grown by MOCVD without growth interruptions. These MOCVD-grown tunnel junctions were optimized for minimization of the tunnel junction voltage drop. Two device structures were studied, an all-GaN homojunction tunnel junction, and a graded InGaN heterojunction-based tunnel junction. This work reports a record-low voltage drop in the graded-InGaN heterojunction based tunnel junction device structure achievi (open full item for complete abstract)

Committee: Siddharth Rajan (Advisor); Shamsul Arafin (Committee Member); Steven Ringel (Committee Member); Hongping Zhao (Committee Member) Subjects: Electrical Engineering

Master of Science (MS), Wright State University, 2020, Physics

Group IV elements based nanoelectronics devices (mainly Si and Ge based devices) have been developed and improved over a long period of time and are the most influencing materials of semiconductor electronics, but due to their indirect bandgap their use in optoelectronics is limited. Alternatively, new Group IV alloys comprised of Ge, Si, and Sn semiconductor materials have emerged as attractive options for various electronic and optoelectronic applications. The binary and ternary alloys provide strain and energy bandgap engineering by controlling element content, a route for realizing direct-transition semiconductors, improvement in interface and defect properties, and a reduction of the process temperature related to the crystal growth. However, there are many obstacles and challenges for the crystal growth of Ge-Sn alloy on the Silicon or Germanium substrate. One of the problems in Ge-Sn growth is Sn precipitation from Ge-Sn. Theoretical calculation predicts that Ge transitions from an indirect semiconductor to a direct semiconductor by incorporation of Sn on Ge matrix. For tensile strained Ge-Sn alloys, the transition is predicted at 6.3% Sn concentration. This is the main driving force for the growth of epitaxial Ge-Sn crystals on Si substrates. The epitaxial growth of Ge-Sn is very challenging because of huge lattice mismatch between Ge and Sn and, the strong surface segregation of Sn on Ge and extremely low equilibrium solubility of Sn on Ge. In the recent past, a lot of progress has been made for the development of epitaxial growth techniques. Besides other techniques like MBE for the deposition of Ge-Sn on the substrate of Si, chemical vapor deposition has been achieved. Similarly, pulsed laser-induced epitaxy is also another technique for the deposition. Besides the experimental efforts to study the Ge-Sn-Si elemental binary and ternary alloys, Molecular Dynamics (MD) modeling provides insight into atomic configurations and structural dynamics, which req (open full item for complete abstract)

Committee: Amit Sharma Ph.D. (Advisor); Brent D. Foy Ph.D. (Committee Member); Sarah F. Tebbens Ph.D. (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2014, Materials Science and Engineering

Over the last two decades, group III-nitride compound semiconductor materials have revolutionized modern optoelectronics and high frequency devices. In this work, III-nitride based compound semiconductor nanostructures with tailor-made optoelectronic and magnetic functionalities are investigated. The first research vector concerns design, synthesis and characterization of novel ferromagnetic materials based on III-nitrides involving manipulation of magnetic dopants as well as heteroepitaxy of ferromagnetic materials. Synthesis of III-nitride-GdN epitaxial, ferromagnetic nanocomposites is developed using the technique of plasma assisted molecular beam epitaxy. Magnetic, structural and optical characteristics of these materials are tailored to yield nanocomposites which preserve the structural and semiconducting characteristics of GaN while integrating the ferromagnetic compound GdN. In the second part of this work, the growth, characterization and development of self-assembled III-nitride nanowire based ultraviolet light emitting diodes is explored. These devices are formed by a novel heterostructure which utilizes synthetic gradients in dipole moment per unit volume to mitigate many of the shortcomings of traditional thin film wide bandgap light emitting diode (LED) device designs for deep ultraviolet wavelengths. The optical and electronic characteristics of these devices are investigated by a number of spectroscopic methods. Combination of this heterostructure with the epitaxy of GdN on III-nitrides is found to yield a unique electrical device which allows electrical modulation of narrow linewidth, ultraviolet Gd intra-f-shell fluorescence at significantly lower voltages compared to existing technology. During the course of this work, a number of unique scientific instruments were developed to aid research efforts in the Myers group. The design, construction and operation of a wide spectral bandwidth, ultrafast semiconductor photoluminescence characterization syst (open full item for complete abstract)

Committee: Myers Roberto (Advisor); Rajan Siddharth (Committee Member); Grassman Tyler (Committee Member) Subjects: Materials Science

PhD, University of Cincinnati, 2003, Engineering : Electrical Engineering

With the continued expansion of electronic information resources, storage capacity requirements are expected to exceed the petabit level for large database and data warehouse systems. Along with the increasing reliance on large capacity memory systems, there will be a demand for more efficient memory access technology. While considerable effort has been devoted toward the development of optical volumetric storage media to meet the growing demand for archival data storage, relatively little work has been done to explore the technological barriers associated with providing page-oriented access to these memory devices. To address this problem in database systems, the concept of a database filter has been suggested. A database filter serves as an interface between a large volume page-oriented optical storage device and an electronic host computer. Based on a smart pixel strategy, the filter performs optical-to-electrical data conversion, processes database query operations and only passes the data matching a query to the host computer. The database filter can offset the bandwidth mismatch without loss of valid data or significant delay in data access. CMOS compatible photonic VLSI device technology is able to provide large photodetector arrays and significant logic complexity. In the dissertation research, the prototype of a 32x32-bit optoelectronic database filter chip has been implemented using a 0.35-micron CMOS technology. The filter monolithically integrates all necessary optoelectronic and logic components, including photodetectors/receivers, data manipulation logic, data queue, filter control circuitry, and interface to the host computer, into a single CMOS chip. The integration will significantly reduce the optical system complexity and yield a compact and robust read head. Queueing theory is used to analyze the performance enhancement introduced by the database filter. It is shown that even with the limitation of finite queue capacity, a database filter could b (open full item for complete abstract)

Committee: Dr. Fred R. Beyette, Jr. (Advisor) Subjects:

MS, University of Cincinnati, 2002, Engineering : Electrical Engineering

In avionic systems, data integrity and high data rates are necessary for stable flight control. Unfortunately, conventional electronic control systems are susceptible to electromagnetic interference (EMI) that can reduce the clarity of flight control signals. Fly-by-Light systems that use optical signals to actuate the flight control surfaces of an aircraft have been suggested as a solution to the EMI problem in avionic systems. Fly-by-Light in avionic systems reduces electromagnetic interference hence improving the clarity of the control signals. Fly-by-Light technology development involves creation of building blocks like computers, fiber optic sensors and interfaces, fiber actuator loops, an integrated system etc. The development of this technology exploits fiber optic sensor and control technology. This thesis demonstrates a hybrid approach that combines a smart silicon photoreceiver module with a SiC power transistor. The resulting device uses a 5mW optical control signal to produce a 150A current that is suitable for driving an electric motor. This is the first attempt to integrate silicon carbide devices with a smart silicon chip. The first part of the thesis deals with the various high power technologies that are in use today. Different approaches are discussed and emphasis is stressed on the silicon/silicon carbide hybrid design. Briefly discussed is the use of silicon carbide for optical switching application. Second part of the thesis involves the design, simulation and analysis of the silicon smart chip. Individual components of the smart silicon are characterized and results shown. Finally, we report the performance evaluation of this smart silicon realized in a 1.5 micron CMOS process using MOSIS foundry service.

Committee: Dr. Fred Beyette, Jr. (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2008, Physics

ZnO has received renewed attention in recent years due its exciting properties as a wide band gap semiconductor. ZnO has several advantages over GaN including the availability of substrates, a room temperature excitonic emission, and an environmentally benign chemistry. ZnO applications include efficient blue light emitters, surface acoustic wave devices, transparent conductors, high power transistors, and solid state white lighting. Despite this versatility, several hurdles remain before device realization. Firstly, ZnO is almost always p-type. Although high quality n-type ZnO is abundant, there is no stable and reliable p-type doping scheme. Secondly, research into high quality Ohmic and Schottky contacts has been limited. Although there is an abundance of literature, there has yet to be an attempt to understand the physical and chemical mechanisms at metal-ZnO interfaces. In this work, plasma processing techniques are adopted to ZnO. These cold plasmas allow for room temperature modification of the subsurface. Implanting hydrogen has identified it as a primary n-type dopant responsible for a large fraction of the n-type conductivity. Oxygen plasma treatment has yielded an Ohmic to Schottky conversion by reducing oxygen defects at the near surface. Deposition of metals on clean and ordered surfaces reveal the importance that defects play at the metal-semiconductor interface. Higher concentrations of defects promote reactions. This increased reaction eutectic forming and oxide forming. Understanding the nature of the metal allows for engineering of high quality blocking contacts. These contacts can provide added thermal stability to devices. Subsurface introduction of hydrogen and nitrogen provide a potential roadmap to p-type doping and high quality Schottky contacts. Overall, control of transport properties and contact integrity is achieved by remote plasma processing.

Committee: Leonard Brillson Prof (Advisor); Jay Gupta Prof (Committee Member); Thomas Humanic Prof (Committee Member); Julia Meyer Prof (Committee Member); Yann guezennec Prof (Committee Member) Subjects: Physics

PHD, Kent State University, 2012, College of Arts and Sciences / Chemical Physics

In this dissertation, research results of two plasmonics related projects will be presented. The first project is mainly focused on modeling the circular and spiral metallic nano-gratings. Their applications in generating azimuthally and radially polarized beam and focusing near field will be discussed. The second project is to design and fabricate various MDM plasmonic cavities and to explore the resonance modes inside the cavities and the excitation conditions of these modes. The potential applications of these studied MDM plasmonic structures in integrated photonics will also be presented.

Committee: Qi-Huo Wei PhD (Committee Chair); Hiroshi Yokoyama PhD (Committee Member); Deng-Ke Yang PhD (Committee Member); Jaroniec Mietek PhD (Committee Member); Mann Elizabeth PhD (Committee Member) Subjects: Physics