Electronic properties of cesium on 6H-SiC surfaces

The adsorption of cesium on clean {0001} surfaces of n- and p-6H-SiC samples at low temperatures was investigated by using Auger electron, x-ray photoelectron, and ultraviolet photoelectron spectroscopy as well as a Kelvin probe. At clean surfaces the Fermi level is pinned at 1.2 eV above the valence-band maximum and the ionization energy measures 5.7 and 5.8 eV on Si- and C-terminated surfaces. At 130 K, cesium grows layer by layer. The films become metallic after the deposition of the first Cs layer. For submonolayer coverages, Cs-induced surface donors form at 2.95 eV above the valence-band maximum. They are due to covalent Cs-Si bonds, The barrier height of Cs/6H-SiC Schottky contacts was found as 0.57+/-0.05 eV with n-type and 2.28+/-0.1 eV with p-type doped samples. These results confirm the concept that the continuum of metal-induced gap states determines the barrier heights of ideal metal-semiconductor contacts. (C) 1996 American Institute of Physics.