HUGE CHARGE-TRANSFER FROM POTASSIUM ON H-SI(111)-(1X1)

Potassium adsorption on the hydrogen-terminated H:SI(111)-(1 x 1) surf ace is studied by high-resolution core-level and valence-band photoele ctron spectroscopy. New light is shed on the interpretation of core-le vel spectra at the K/Si(111) interface. Low potassium coverages induce a large downward band bending. The Fermi level moves similar to 0.26 eV above the conduction band minimum, which is explained by a huge cha rge transfer from the adsorbate to the semiconductor bulk, For room-te mperature saturation coverage, the Fermi level drops back into the sem iconductor band gap. This leads to a vanishing n-type Schottky barrier height Phi((n)) = 0.02 +/- 0.03 eV in agreement with theoretical resu lts. (C) 1998 Elsevier Science B.V. All rights reserved.