Surface and interface structures of S-passivated GaAs(111) studied by soft x-ray standing waves

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Abstract
Surface and interface structures of S-passivated GaAs(111)A and (111)B with and without CaF2 overlayers have been investigated using the soft x-ray standing-wave technique. On the GaAs(111)A surface S atoms are located on top of the first layer Ga atoms, while on the GaAs(111)B surface S atoms replace the first layer As atoms. This is in agreement with the photoemission results. It is found that CaF2 deposition and post-annealing does not change the position of S atoms. A well-ordered S structure for S/GaAs(111)B is maintained, indicating a high stability of S—Ga bonds. This is in contrast to the low coherent fraction for the S interlayer atoms observed from the CaF2/S/GaAs(111)A system.