Abstract
The chemical and electronic properties of selenium passivatedGaAs(001)-2 × 1 surfaces were investigated by a combination of theoretical calculations and core levelphotoemission experiments. An anion exchange results in gallium-selenide like layers showing a2 × 1 reconstruction in low energy electron diffraction (LEED). The analysis of the different components inthe core level spectra of As 3d, Ga 3d and Se 3d limits the number of possible structural models. TheSe/GaAs(001)-2 × 1 reconstruction has been also analysed by means of DFT-LDA calculations andtheoretical STM currents. In a first step, different geometries are considered andthe most stable one, from the point of view of the thermodynamic potential, isdetermined. Then, STM currents and the corresponding surface corrugation arecalculated and compared with the experimental evidence. We conclude that theSe/GaAs(001)-2 × 1 reconstruction has a single Se atom in the last crystal layer, bonded to two Ga atoms of thesecond layer, and another Se layer replacing the third As layer of the crystal. Thesesurfaces may be considered as chemically stable because they withstand considerableexposure to air. In terms of electronic passivation, i.e. the removal of any surface bandbending, the selenium modification is not successful. Band bending on n-type dopedsamples is reduced while band bending on the p-type doped samples is further increased.
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