ELECTRONIC-STRUCTURES OF AS SI(001) 2X1 AND SB/SI(001) 2X1 SURFACES/

The electronic structures of the As/Si(001) 2x1 and Sb/Si(001) 2x1 sur faces with symmetric dimers are calculated self-consistently with the use of planar basis functions made of two-dimensional plane waves and one-dimensional Gaussian functions, based on local-density-approximati on and norm-conserving pseudopotentials. The calculations show that bo th the As/Si(001) 2x1 and Sb/Si(001) 2x1 surfaces are semiconductors w ith energy gaps of about 1.0 eV. Both As and Sb surface bands have sim ilar dispersion and are very different from that of the Si(001) 2x1 su rface. The calculated dispersion of surface states for As/Si(001) is i n good agreement with the angle-resolved photoemission measurements. T he calculated work functions are 5.56 eV and 4.03 eV for As/Si(001) an d Sb/Si(001) surfaces, respectively. We find substantial charge transf er for the As/Si(001) surface, indicating a strong ionic character in the Sb-Si bonds. The strong polar covalent bonding between surface As atoms and underlying Si atoms may be responsible for the stability of the As/Si(001) surface.