| dc.description.abstract | 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. | en_US |
