Gallium nitride on low temperature cofired ceramic templates for Schottky junctions

In this work aluminum, silicon and zinc oxide were used as intermediate layers for thin film growth on cofired glass ceramic substrates. The motivation behind this work is a direct deposition of nitride thin films on the surface of the ceramic substrate, eliminating the die and attach techniques. Ceramics have unique applications due too the nature of their mechanical processing, and their physical resilience and chemical inertness. The low melting of the glass ceramics from a device processing perspective and their rough, inhomogeneous surface presents a challenge for device fabrication. Oxide materials can be applied by a variety of techniques compatible with large device areas and arbitrary shapes to apply a surface texture to improve thin film properties for device fabrication. Ideally these techniques could be applied to any substrate that meets the thermal budget of the thin film process. Solution coating was found to be a good candidate for applying coatings since it can deposit many different oxide materials over large areas, for relatively low cost, and surface tension of the liquid phase helps to planarize the surface. Several (>7) microns of coating materials were found to be needed to reduce the appearance of the ceramic surface features. Deposition of GaN on the surface of the oxide coatings was performed using a Flow Modulation Epitaxy (FME) style deposition in conjunction with a unique hollow cathode plasma source. These features are designed to lower the overall temperature requirements for GaN growth by providing additional Ga migration time during growth and by using nitrogen plasma as an alternative to thermal decomposition of ammonia. Ni/Au Schottky junctions fabricated on sapphire using ceramic compatible temperatures and FME show leaky characteristics with high ideality factors, indicating tunneling is a significant contributor to carrier transport through the junction. The same Ni/Au GaN devices fabricated on ZnO coated ceramics was found to produce ohmic junctions. The density of surface states is a likely candidate for this behaviour

Engineering of III-nitride semiconductors on low temperature Co-fired ceramics

This work presents results in the field of advanced substrate solutions in order to achieve high crystalline quality group-III nitrides based heterostructures for high frequency and power devices or for sensor applications. With that objective, Low Temperature Co-fired Ceramics has been used, as a non-crystalline substrate. Structures like these have never been developed before, and for economic reasons will represent a groundbreaking material in these fields of Electronic. In this sense, the report presents the characterization through various techniques of three series of specimens where GaN was deposited on this ceramic composite, using different buffer layers, and a singular metal-organic chemical vapor deposition related technique for low temperature deposition. Other single crystalline ceramic-based templates were also utilized as substrate materials, for comparison purposes

Low Temperature Epitaxial Growths of III-Nitride Semiconductors on ITO Glass Substrates

Chapter 1 serves as an introduction to the electronic, optical and physical properties of the nitride material system that have made it a heavily researched group of semiconductors. The need for heteroepitaxy and various commercially successful substrates will be discussed along with the motivation of this thesis. Some general history will be provided as well as the challenges faced by these materials in commercialization. Chapter 2 will focus on current and past growth techniques used for nitrides, outlining how epitaxy occurs in these systems with their respective benefits and faults. Chapter 3 will give an overview on the characterization tools used throughout this research. An understanding of how these tools operate will assist in interpreting data correctly. Combined with knowledge from chapter 2 it may also give insight on what needs to change about growth conditions to optimize growth. Chapter 4 will present the growth results from various characterization tools discussed in chapter 3. Conclusions about the data from each material system will be discussed. Chapter 5 will focus on theoretical calculations for InN. Initial results for InN show it to be the most promising material. A theoretical analysis of common impurities on the electronic band structure of InN will help in interpreting optical properties of the material. The central research contributions of the author in this thesis can be summarized as the development of III-Nitrides growth recipes for each material, characterization of the results, and the application of LCAO theory to the InN system for common impurities found in the growth technique examined