Molecular beam epitaxy of AlScN on Si(111)

Wurtzite aluminum scandium nitride thin films are a leading candidate material for the development of next-generation semiconductor electronic, photonic, and acoustic devices. The integration of high-quality AlScN thin films on a silicon platform is of scientific and commercial interest. Here, we report the successful epitaxial growth of crack-free metal-polar AlScN thin films on (111) silicon substrates by plasma-assisted molecular beam epitaxy. We identify critical nucleation conditions for smooth morphology and growth parameters for high crystal quality and stress mitigation. Using an AlN nucleation layer grown under nitrogen-rich conditions and compositionally graded AlScN buffer layers, we obtain single-phase films with narrow 002 rocking curve FWHM as low as 0.51°, crack-free films up to 150 nm thick with ScN fraction as high as 31%, and surface RMS roughness as low as 0.54 nm over 400μm2, which follow the morphology of the underlying silicon substrates with a mixed 2D–3D growth mode. The lattice parameters, d33 piezoelectric coefficients, and optical bandgap are measured as a function of Sc composition. With increasing Sc composition, the piezoelectric coefficient is enhanced to as high as 34.7 pm/V.