Scandium nitride is a semiconductor, which like silicon can be used for electronic devices, but has rarely been studied. This project focuses on making single crystals of scandium nitride that are free of defects and with low concentrations of impurities, as this is necessary for studying intrinsic properties of this material and determining its potential for future device applications such as light emitting diodes and high-temperature electronics. Scandium nitride crystals have been difficult to produce because of its very high melting temperatures. The crystal growth method used in this research, physical vapor transport, produces larger, better quality scandium nitride crystals than previously employed methods. Graduate students supported by this project are receiving hands-on research training while making new scientific discoveries and developing new technologies. This project also introduces young women (12 to 14 years old) to the science and technology of crystal growth and semiconductors, through the K-State Girls Researching Our World summer workshops.
Single crystals of scandium nitride (ScN) with no or significantly fewer defects are grown to explore the intrinsic electrical properties of this semiconductor. To achieve this goal, the specific activities of the research are as follows. First, the process of crystal growth by physical vapor transport is optimized by adjusting the furnace temperature, pressure, and configuration to produce material with low defect densities and low impurity concentrations. These experiments are guided by thermodynamic and transport phenomena modeling. Second, the electrical properties of ScN are measured and correlated with the temperature and impurity concentrations, to reveal its electrical conduction energetics. Specifically, the electron mobility and charge carrier concentrations are determined by temperature-dependent Hall effect measurements and are correlated with the crystal defect densities (determined by defect sensitive etching), deviations from stoichiometry, and impurity concentrations (measured by secondary ion mass spectrometry). Third, selected impurities are intentionally added to scandium nitride to determine how they change its electrical properties. Differences in the properties caused by the crystal orientation and polarity (nitrogen or scandium) are investigated. By correlating these measurements with the process conditions, methods of controlling ScN's electrical properties are under development. This study provides valuable intrinsic electrical properties of ScN for future device explorations.
