Evidence for the passivation effect in (NH4)2Sx-treated GaAs observed by slow positrons

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Abstract
We applied slow positrons to the as‐etched GaAs and/or the (NH4)2Sx‐treated GaAs. The results show that a thin oxide film is easily formed on the surface of as‐etched GaAs as soon as the etched surface is exposed to air for several minutes before the measurement. On the other hand, the monolayer of chemisorbed sulfur atoms in the (NH4)2 Sx‐treated GaAs is effective in protecting the clean surface from the adsorption of oxygen atoms. The mean diffusion length of positrons is not affected by the conditions of the surface treatment. This implies that the centers for the trapping of a positron are not created below the free surface by those treatments.