Se/GaAs(110): Atomic and electronic structure

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Abstract
The molecular-beam deposition of selenium onto ultrahigh-vacuum cleaved GaAs(110) surfaces and subsequent annealing leads to the formation of a thin, stable, Se-rich reacted layer with distinct structural and electronic properties. We perform ab initio calculations based on density-functional theory of the Se-deposited GaAs(110) surface for different coverages, FTHETA=1/4, 1/2, 1, and 3/2, and various structural models. In the FTHETA=1/4 case we give a detailed analysis of the total-energy surface of the Se/GaAs(110) system. The highest adsorption energy is found for Se atoms bound in an interchain bridging position. For higher coverages we discuss a variety of adsorption models and compare these with exchange reactions in terms of the thermodynamic stability. We observe a tendency for an exchange of As and Se atoms in the uppermost layers and subsequent segregation of As at the surface. For the energetically most favored structures, we compare the calculated band structures with data from soft-X-ray photoemission spectroscopy.