Core threshold photoemission spectroscopy from the As 3d core level of GaAs (110) and effects of Ge chemisorption

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Abstract
We have investigated the excitation of the As 3d core level of clean and Ge covered GaAs (110) surfaces into low lying conduction band states by observing core-hole decay emission. The investigation was carried out by using synchrotron radiation to record photoemission spectra in the CIS and EDC modes. In contrast to the Ga 3d core excitation, the As 3d core excitation was found to be nonexcitonic in character. The CIS shows three structures at hυ = 43.0, 46.1, and 49.5 eV, which were strongly influenced by Ge-chemisorption. With about a monolayer of Ge, the structures are reduced to a considerably larger degree than the photoemission structure associated with the Ga 3d exciton. The As 3d core level is excited into surface related p-like states lying 2.6, 5.7, and 9.1 eV above the valence band maximum, ’’followed’’ by the radiationless Auger decay of the core holes. The inferred conduction band states are compared to recent band calculations and the state at 2.6 eV is assigned to the Ga-dangling-bond surface state. With the assumption that the As 3d core excitation is to the same surface state as the Ga 3d core excitation, we estimate the exciton binding energy for the latter excitations to be ∠1.8 eV.

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