Joseph Kolthammer with Kathy Kash

Near-Atmospheric Thermal Gradient Growth of Single Crystal Gallium Nitride

Gallium nitride (GaN) is a highly desirable wide bandgap semiconductor with myriad optoelectronic applications. Reliable GaN growth has in the past been limited to reactions at 10 kbar or greater pressures; a near-atmospheric process features much easier implementation. The first objective of this project is the construction of a reactor to support the growth of a polycrystalline GaN seed crust from a molten gallium phase using ammonia as the nitrogen source. The seed crust will form at the top of the melt in a small graphite crucible. Numerical modeling indicates that under the influence of a thermal gradient, and the consequent solubility gradient, single crystal GaN may grow into the melt from the polycrystalline seed, like a stalactite from a cave ceiling. Upon successful synthesis, the material will be characterized with a variety of techniques. A reliable thermal gradient growth mechanism would be applicable in the experimental growth of many other semiconductors, and the growth process could easily be enlarged to production scale.