Hexagonal Boron Nitride Crystal Growth from Solution: A Study of Fundamentals

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Solid state electronic devices such as diodes and transistors used in cell phones, computers, and light emitting diodes (LEDs) require materials of the highest perfection. They must be close to flawless and have low impurity concentrations in order for the device to function properly. Under this award, a method of producing single crystals of a new electronic material, hexagonal boron nitride, with high perfection will be developed. Currently, this material is only available as a powder, but much larger crystals are necessary for many applications. In this research program, hexagonal boron nitride crystals will be produced from a molten metal solution as it is cooled from a high temperature. The effect of parameters such as the solution's maximum temperature and cooling rate on the size and perfection of the crystals will be determined. High quality hexagonal boron nitride single crystals are expected to enable new types of electronic devices, such as ultraviolet light emitting diodes for water purification and sterilizing medical equipment, flexible electronics, and radiation sensors for interdicting materials to make nuclear weapons.The processing parameters that affect the size and quality of hexagonal boron nitride single crystals precipitated from a molten nickel-chromium solvent will be examined by the statistical response surface methodology. Solution growth was selected due to its relatively low temperature (1600 C) and pressure ( 1 atmosphere) requirements. The boron and nitrogen concentrations, the maximum temperature of the solution, and the solution cooling rate are expected to be important parameters. The concentrations and distributions of boron and nitrogen (as pairs or isolated elements) in the solution will be measured as a function of temperature. The impact of temperature and supersaturation on the crystal's growth rate, area, thickness, habit, surface morphology, and dislocation types and densities will be determined by a combination of optical and electron microscopy, x-ray diffraction, and compositional analysis. The influence of impurities (specifically oxygen and carbon) on the growth rate anisotropy and crystal habit will also be examined. This investigation will establish the fundamental thermodynamic and kinetic parameters that are most important for controlling the size and quality of hexagonal boron nitride single crystals so the process can be optimized. It will support the education of a PhD student and will provide high quality materials to other researchers to investigate hexagonal boron nitride's optical, electrical, and mechanical properties and applications.