Soft-x-ray photoemission study of chemisorption and Fermi-level pinning at the Cs/GaAs(110) and K/GaAs(110) interfaces.

Abstract

The room-temperature adsorption of Cs on n-type GaAs(110) has been studied with use of core-level photoelectron spectroscopy. The coverage-dependent splitting of the Cs 4d core level into two sets of doublets indicate site-dependent adsorption for submonolayer coverages up to about 0.5 monolayer (ML). The broadening of this core level close to the saturation coverage is consistent with the growth of an out of registry monolayer as suggested by low-energy electron diffraction (LEED) data. Analysis of the substrate core levels indicate the formation of a laterally uniform overlayer and lack of chemical reaction. The Schottky barrier of 0.7 eV obtained from the low-coverage band bending is similar to the values for many other metals with much larger work function (Al, Ni, or Ti). We report also data on the K overlayers. They indicate a similar value of band bending and presence of a chemical reaction at the K/GaAs interface. The band bending results for Cs and K indicate that Schottky barrier for GaAs interfaces do not depend on the metal work function in a very broad range of the work-function values.