Photoemission study of chemisorption and Fermi-level pinning at K/GaAs(1Â 0Â 0) interface with synchrotron radiation

The adsorption of K on the n-GaAs(1 0 0) surface was investigated by X-ray photoelectron spectroscopy (XPS) and synchrotron radiation photoemission spectroscopy (SR-PES). The Ga3d and As3d core level was measured for clean and K adsorbed GaAs(1 0 0) surface. The adsorption of K induced chemical reaction between K and As, and the K-As reactant formed when the K coverage θ > 1 ML. The chemical reaction between K and Ga did not occur, but Ga atoms were exchanged by K atoms. From the data of band bending, the Schottky barrier is 0.70 eV. The Fermi-level pinning was not caused by defect levels. The probable reason is that the dangling bonds of surface Ga atoms were filled by the outer-shell electrons of K atoms, forming a half-filled surface state. The Fermi-level pinning was caused by this half-filled surface state.