The microstructure, dielectric, and pyroelectric properties of AlxGa1-xN composite epitaxial layers grown on SiC / (111) Si substrates by chloride-hydride epitaxy are studied. In the process of layer growth, the phenomenon of spontaneous formation of heterojunctions was discovered. Based on AlxGa1-xN epitaxial layers, a material has been obtained which currently has one of the highest pyroelectric coefficients for crystals (or thin films) of aluminum nitride.