Investigation Of Europium Doped Wide Band Gap Oxides And An Annealing Study Of The Amorphous Oxide Semiconductor Indium Gallium Zinc Oxide

Keywords: pulsed laser deposition, gallium oxide, PLD, indium gallium zinc oxide, wide bandgap oxide, wide band gap oxide, gadolinium oxide, IGZO, oxide, wide band gap, europium, wide bandgap, annealing.

The electronic, optical and luminescent properties of europium doped wide band gap oxide thin films and the electronic properties of indium gallium zinc oxide (IGZO), a novel amorphous oxide semiconductor were investigated. The thin films of europium doped gallium and gadolinium oxides and indium gallium zinc oxide were deposited on c-axis oriented sapphire substrates by Pulsed Laser Deposition at various conditions of temperature, pressure and doping concentration. Europium doped gallium oxide was found to be in beta phase with monoclinic crystal structure and the films exhibited intense red emission under cathode ray excitation with a peak wavelength of emission at 611 nm which corresponds to the transitions from 5D0 to 7F2 levels in europium. Europium doped gadolinium oxide thin films were found to exhibit two different phases (cubic and monoclinic) with the one of the phases being dominant depending on the growth conditions. The peak wavelength of emission was either 611 nm or 613 nm depending on the phase of the films. The amorphous indium gallium zinc oxide thin films were found to exhibit very high hall mobilities of the order of ̃15 cm2∙V−1∙s−1 and the conductivity could be controlled over several orders of magnitude from 5 x 10−3 S∙cm−1 to 10 S∙cm−1 in the amorphous phase. Annealing the films in presence of air was found to decrease the carrier concentration of the films due the incorporation of oxygen in the films thereby filling up the oxygen vacancies. Applications of amorphous indium gallium zinc oxide include Transparent Thin Film Transistors and use as transparent conducting oxide for optoelectronic devices.

Gallium oxide has been recognized as a promising Ultrawide-Bandgap(UWBG) semiconductor with a band gap ranging from 4.3-5.3eV. Beta gallium oxide, a polymorph of Gallium Oxide, has an ultra-wide bandgap of 4.9eV making it a great candidate for next-generation power electronics. In addition, UWBG semiconductors are capable of large breakdown voltage and has the potential of becoming a high-effciency switching device. The electrical characteristics are then analyzed using a Hall effect. Some samples are often annealed or doped to improve their electrical properties. The work presented in this thesis shows the process of recently developed gallium oxide flms with a focus on indium gallium oxide samples. The result of our research shows that signifcant changes to the electrical properties of gallium oxide films can be achieved through doping and annealing. In order to utilize the powerful properties of gallium oxide, this work incorporated indium to grow indium gallium oxide. Homogeneous and heterogeneous samples of indium gallium oxide were grown on the MOCVD with a unique recipe that allowed for controlled precursor injection. Furthermore, growth parameters were varied to test their effectiveness in the interplay between indium oxide and gallium oxide growth. The samples were then characterized using X-ray Diffraction(XRD) and Hall effect system. The XRD system allows for further understanding between the growth parameters and the resulting structure of the material. The combination of the XRD system and Hall effects allows for a great correlation between the MOCVD growth parameters and the resulting film qualities. Samples are annealed in hydrogen to enhance their electrical properties. Our experiments demonstrate enhanced electrical characteristics and even p-type conductivity can be produced with effective growth processing.

AMORPHOUS OXIDE SEMICONDUCTORS A singular resource on amorphous oxide semiconductors edited by a world-recognized pioneer in the field In Amorphous Oxide Semiconductors: IGZO and Related Materials for Display and Memory, the Editors deliver a comprehensive account of the current status of—and latest developments in—transparent oxide semiconductor technology. With contributions from leading international researchers and exponents in the field, this edited volume covers physical fundamentals, thin-film transistor applications, processing, circuits and device simulation, display and memory applications, and new materials relevant to amorphous oxide semiconductors. The book makes extensive use of structural diagrams of materials, energy level and energy band diagrams, device structure illustrations, and graphs of device transfer characteristics, photographs and micrographs to help illustrate the concepts discussed within. It also includes: A thorough introduction to amorphous oxide semiconductors, including discussions of commercial demand, common challenges faced during their manufacture, and materials design Comprehensive explorations of the electronic structure of amorphous oxide semiconductors, structural randomness, doping limits, and defects Practical discussions of amorphous oxide semiconductor processing, including oxide materials and interfaces for application and solution-process metal oxide semiconductors for flexible electronics In-depth examinations of thin film transistors (TFTs), including the trade-off relationship between mobility and reliability in oxide TFTs Perfect for practicing scientists, engineers, and device technologists working with transparent semiconductor systems, Amorphous Oxide Semiconductors: IGZO and Related Materials for Display and Memory will also earn a place in the libraries of students studying oxides and other non-classical and innovative semiconductor devices. WILEY SID Series in Display Technology Series Editor: Ian Sage, Abelian Services, Malvern, UK The Society for Information Display (SID) is an international society which has the aim of encouraging the development of all aspects of the field of information display. Complementary to the aims of the society, the Wiley-SID series is intended to explain the latest developments in information display technology at a professional level. The broad scope of the series addresses all facets of information displays from technical aspects through systems and prototypes to standards and ergonomics.

Flat panel displays have become ubiquitous, enabling products from highresolution cell phones to ultra-large television panels. Amorphous silicon (a- Si) has been the industry workhorse as the active semiconductor in pixeladdressing transistors due to its uniformity and low production costs. However, a-Si can no longer support larger and higher-resolution displays, and new materials with higher electron mobilities are required. Amorphous indium gallium zinc oxide (a-IGZO), which retains the uniformity and low cost of amorphous films, has emerged as a viable candidate due to its enhanced transport properties. However, a-IGZO devices suffer from long-term instabilities—the origins of which are not yet fully understood—causing a drift in switching characteristics over time and affecting product lifetime. More recently, devices fabricated from textured nanocrystalline IGZO, termed c-axis aligned crystalline (CAAC), have demonstrated superior stability. Unfortunately, little is known regarding the phase formation and crystallization kinetics of either the CAAC structure or in the broader ternary IGZO system. Crystallinity and texture of CAAC IGZO films deposited by RF reactive sputtering were studied and characterized over a wide range of deposition conditions. The characteristic CAAC (0 0 9) peak at 2 = 30 was observed by X-ray diffraction, and nanocrystalline domain texture was determined using a general area detector diffraction system (GADDS). Highly ordered CAAC films were obtained near the InGaZnO4 composition at a substrate temperature of 310C and in a 10%O2/90% Ar sputtering ambient. High-resolution transmission electron microscopy (HRTEM) confirmed the formation of CAAC and identified 2– 3 nm domains coherently aligned over large ranges extending beyond the field of view (15 nm 15 nm). Cross-section HRTEM of the CAAC/substrate interface shows formation of an initially disordered IGZO layer prior to CAAC formation, suggesting a nucleation mechanism similar to ZnO thin films. A classical nucleation and growth model is proposed and compared to alternative models proposed in literature. Extending this study of CAAC IGZO, the formation and growth of crystalline IGZO over a wide composition range and processing conditions were explored. IGZO itself is one composition of a class of homologous structures in the pseudo-binary InGaO3(ZnO)m system. For integer m, the equilibrium structure is known and well-characterized; however, for non-integer m, disorder must exist and the kinetics of the structural development remain almost completely unknown. A high-throughput (combinatorial) approach utilizing co-sputter deposition, millisecond timescale thermal gradient laser annealing, and spatially-resolved characterization using microbeam wide-angle X-ray scattering was used to probe the structural evolution as a function of temperature, time, and composition. As-deposited films were amorphous in the InGaO3- rich composition range, becoming crystalline (wurtzite) with increasing ZnO content. Under millisecond heating, films evolved toward the equilibrium layered structure consisting of nearly pure In2O3 layers with (Ga, Zn)Ox interlayers.

Gallium Oxide: Technology, Devices and Applications discusses the wide bandgap semiconductor and its promising applications in power electronics, solar blind UV detectors, and in extreme environment electronics. It also covers the fundamental science of gallium oxide, providing an in-depth look at the most relevant properties of this materials system. High quality bulk Ga2O3 is now commercially available from several sources and n-type epi structures are also coming onto the market. As researchers are focused on creating new complex structures, the book addresses the latest processing and synthesis methods. Chapters are designed to give readers a complete picture of the Ga2O3 field and the area of devices based on Ga2O3, from their theoretical simulation, to fabrication and application. Provides an overview of the advantages of the gallium oxide materials system, the advances in in bulk and epitaxial crystal growth, device design and processing Reviews the most relevant applications, including photodetectors, FETs, FINFETs, MOSFETs, sensors, catalytic applications, and more Addresses materials properties, including structural, mechanical, electrical, optical, surface and contact

In this work, a body of knowledge is presented which pertains to the growth, characterization and exploitation of high quality, novel II-IV oxide epitaxial films and structures grown by plasma-assisted molecular beam epitaxy. The two compounds of primary interest within this research are the ternary films Ni[subscript x]Mg1[subscript x]O and Zn[subscript x]Mg1[subscript x]0 and the investigation focuses predominantly on the realization, assessment and implementation of these two oxides as optoelectronic materials. The functioning hypothesis for this largely experimental effort has been that these cubic ternary oxides can be exploited--and possibly even juxtaposed--to realize novel wide band gap optoelectronic technologies. The results of the research conducted presented herein overwhelmingly support this hypothesis in that they confirm the possibility to grow these films with sufficient quality by this technique, as conjectured. Ni[subscript x]Mg1−[subscript x]O films with varying Nickel concentrations ranging from x = 0 to x = 1 have been grown on lattice matched MgO substrates (lattice mismatch [epsilon][less than]0.01) and characterized structurally, morphologically, optically and electrically. Similarly, cubic Zn[subscript x]Mg1−[subscript x]0 films with Zinc concentrations ranging from x = 0 to x[almost equal to]0.53, as limited by phase segregation, have also been grown and characterized. Photoconductive devices have been designed and fabricated from these films and characterized. Successfully engineered films in both categories exhibit the desired deep ultraviolet photoresponse and therefore verify the hypothesis. While the culminating work of interest here focuses on the two compounds discussed above, the investigation has also involved the characterization or exploitation of related films including hexagonal phase Zn[subscript x]Mg1−[subscript x]O, ZnO, Cd[subscript x]Zn1−[subscript x]O and hybrid structures based on these compounds used in conjunction with GaN. These works were critical precursors to the growth of cubic oxides, however, and are closely relevant. Viewed in its entirety, this document can therefore be considered a multifaceted interrogation of several novel oxide compounds and structures, both cubic and wurtzite in structure. The conclusions of the research can be stated succinctly as a quantifiably successful effort to validate the use of these compounds and structures for wide bandgap optoelectronic technologies.

Crystalline semiconductors in the form of thin films are crucial materials for many modern, advanced technologies in fields such as microelectronics, optoelectronics, display technology, and photovoltaic technology. Crystalline semiconductors can be produced at surprisingly low temperatures (as low as 120C) by crystallization of amorphous semicon