Angle-resolved ultraviolet photoelectron spectroscopy study on the α-Si(1 1 1)3×3-Bi surface

We have investigated the electronic structure of the Si(1 1 1)3×3-Bi surface with 1/3 ML coverage (the α-3-Bi surface) using angle-resolved photoelectron spectroscopy and low-energy electron diffraction. Three occupied surface localized states (SL1, SL2, and SL3) and some other surface related states (DS and SR) were observed. The SL1 band of three prominent surface localized state bands is found to be located in the bulk band gap over entire k∥ with band width of 0.7 eV and does not cross the Fermi level. This band behavior is in accord with the S1 band of the 3-Sn surface. It is found that the α-3-Bi surface is semiconducting and has the band gap of 1.1 eV. The SL2 and SL3 bands appear only in the restricted k∥ region and the most parts are superposed on the bulk band. The energy separation of the SL2 and SL3 bands is observed to be very small, near the M̄′ point unlike the 3-III and IV surfaces.