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 surfaces 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-approximation and norm-conserving pseudopotentials. The calculations show that both the As/Si(001) 2x1 and Sb/Si(001) 2x1 surfaces are semiconductors with energy gaps of about 1.0 eV. Both As and Sb surface bands have similar dispersion and are very different from that of the Si(001) 2x1 surface. The calculated dispersion of surface states for As/Si(001) is in good agreement with the angle-resolved photoemission measurements. The calculated work functions are 5.56 eV and 4.03 eV for As/Si(001) and Sb/Si(001) surfaces, respectively. We find substantial charge transfer 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.