Nonmetallic behavior of Cs/GaAs(110)

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Abstract
Adsorption of cesium on a GaAs(110) surface is studied, as a function of coverage, using the first-principles linearized augmented-plane-waves-calculation method and a jellium-slab model. For submonolayer coverage, cesium electrons are polarized to the interface by the surface states and surface resonances and do not undergo a Mott transition up to one monolayer. Compared with alkali-metal atoms on metal surfaces, the chemisorption bond for Cs/GaAs(110) goes into a much deeper region of the substrate due to less screening in the semiconductor, leading to substantial electron transfer to the substrate. The coverage dependence of the work function is also obtained and is in accordance with experimental measurements. Furthermore, our results support the idea that metal-induced gap states are responsible for the Fermi-level pinning. Comparison of various properties with Cs/W(100) are made and the essential differences between the semiconductor and metal surfaces are discussed.