Abstract
Cleaved GaAs(110) surfaces were exposed to molecular oxygen in the range from 10 to 10 4 L at temperatures between 60 and 300 K. The interaction was investigated by using a Kelvin probe which measured the contact potential. This method does not deposit energy on the sample and should not influence the oxidation process. To avoid surface photovoltage effects or photon-stimulated adsorption and desorption, the samples were kept in the dark during exposures as well as during measurements. With p-GaAs samples, the work function showed little variation irrespective of temperature while on n-GaAs surfaces kept above 190 K it was observed to increase as a function of oxygen exposures. These findings are attributed to oxygen-induced surface acceptors. Below 190 K only small changes of the work function were observed. This result indicates that chemical reactions are suppressed at low temperatures. The work function of n-GaAs surfaces, which were exposed to oxygen below 160 K and then warmed up, was found to increase. Between 190 and 220 K the work function changed more rapidly with sample temperature. These results again demonsrate that effective chemisorption of oxygen on GaAs(110) surfaces sets in above approximately 190 K. The temperature dependence of the work function can be understood by assuming a precursor state.
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