Molecular beam epitaxy control of the structural, optical, and electronic properties of ScN(001)

Scandium nitride (001) oriented layers have been grown on magnesium oxide ( 001) substrates by molecular beam epitaxy using a rf-plasma source and a sc andium effusion cell. The Sc/N flux ratio is found to be critical in determ ining the structural, optical, and electronic properties of the grown epita xial layers. A distinct transition occurs at the point where the Sc/N flux ratio equals 1, which defines the line between N-rich and Sc-rich growth. U nder N-rich conditions, the growth is epitaxial, and the surface morphology is characterized by a densely packed array of square-shaped plateaus and f our-faced pyramids with the terraces between steps being atomically smooth. The films are stoichiometric and transparent with a direct optical transit ion at 2.15 eV. Under Sc-rich conditions, the growth is also epitaxial, but the morphology is dominated by spiral growth mounds. The morphology change is consistent with increased surface diffusion due to a Sc-rich surface. E xcess Sc leads to understoichiometric layers with N vacancies which act as donors. The increased carrier density results in an optical reflection edge at 1 eV, absorption below the 2.15 eV band gap, and a drop in electrical r esistivity. (C) 2001 American Institute of Physics.