Surface and bulk electronic structure of ScN(001) investigated by scanning tunneling microscopy/spectroscopy and optical absorption spectroscopy

ScN(001) 1x1 surfaces have been prepared by growing ScN on MgO(001) using radio frequency molecular beam epitaxy. In situ ultrahigh vacuum scanning tunneling spectroscopy indicates that the Fermi level at the surface lies slightly above the Sc 3d conduction band edge, which is attributed to a downward band bending at the surface. In situ scanning tunneling microscopy is used to image the Sc and N atom sublattices. While only one atom (Sc) appears at small negative bias, both atoms (Sc and N) appear at certain positive sample biases due to the partially ionic nature of the bonding. Charge accumulation near ionized subsurface donors is evident from the long-range topographic distortions at the surface. The combination of tunneling spectroscopy and optical absorption results show that ScN has an indirect bandgap of 0.9+/-0.1 eV and a direct transition at 2.15 eV.