Disclosed are new methods for the epitaxial growth and deposition of crack-free single-crystalline group-III-nitride (III-N) semiconductor films including AlN and AlGaN on Si substrates to address the current technical challenges in high-quality ultrawide-bandgap semiconductor materials and devices. In this invention disclosure, we introduce several schemes of (1) epitaxial metallic interlayers and (2) superlattice structure consisting of alternating AlN and metal layers between Si (111) substrate and III-N thin film to reduce the in-plane tensile strain or to change the strain to in-plane compressive strain in the film. (3) We also introduce a new route of epitaxial lift-off using water for the film transfer process. This approach offers a new opportunity to overcome the technical challenges of III-N devices for electronic, photonic, energy, and sensing applications with improved performance characteristics and functionalities while reducing manufacturing costs.