The objective of the proposed research is to investigate the properties of the Sc catalytic effect, explore the effects of growth conditions on the mass density of Sc-containing films, and characterize the electrical properties of ScAlN across different film densities to aid in material quality optimization for ScAlN-based HEMTs. A deeper understanding of the impact of substrate temperature and III/V ratio on ScAlN growth kinetics, crystalline quality, and electrical properties enables more precise control over ScAlN growth conditions and thus facilitates material quality optimization and further improvements to the performance of ScAlN-based devices. Preliminary work toward this proposal has demonstrated that ScN, a building block of ScAlN,  grown at increasing substrate temperatures shows an increase in mass density, a property that may affect lattice parameters and apparent growth rate. Additionally, ScN appears to consume significantly more nitrogen per metal modulated epitaxy (MME) cycle than GaN and AlN, supporting the theory of a Sc catalytic effect on the cracking of molecular nitrogen. Building upon these preliminary findings, the research proposed herein further investigates the properties of the Sc catalytic effect, explores changes in film density, and characterizes ScAlN electrical properties as a function of film density toward the development of improved-quality ScAlN-based HEMTs.