PHOTOEMISSION-STUDY OF THE SI(111)3X1-K SURFACE

Surface electronic states of the Si(111)3 X 1-K surface are studied by means of angle-resolved ultraviolet photoelectron spectroscopy along the [112BAR] and the [101BAR] directions. It is found that the S1 state (approximately 0.2 eV below the Fermi level) of the 7 X 7 surface disappears and surface states S2' and S3' appear near the binding energy of approximately 0.9 and approximately 1.8 eV below the Fermi level in the spectra of the Si(111)(3 X 1)-K surface. Hence, the Si(111)3 X 1-K surface is no longer metallic like the Si(111)7 X 7 clean surface but is semiconducting. The saturation coverage of K on the Si(111)3 X 1-K surface is estimated to be 1/3 ML from comparison of the Si LVV Auger spectrum and the K 2p x-ray-photoemission-spectroscopy peak intensity ratio to that of the Si(111)delta7 X 7-K surface. From these results, we suggest a surface geometrical structural model for the Si(111)3 X I-K surface.