Positron interactions with overlayers of oxygen on GaAs(100)

The positron work-function, re-emission yield, and positronium fraction of an n-doped GaAs(100) surface were measured as a function of oxygen exposure. The energy distribution of positrons observed to be re-emitted indicated that the clean and oxygen exposed n-doped GaAs(100) surfaces had negative positron work-functions. The fraction of incident positrons re-emitted as bare positrons, (Y), was found to increase and the fraction re-emitted as positronium, (fPs), to decrease with increasing oxygen exposure. This suggests that surface modified GaAs may be useful as a contact material in the fabrication of GaAs based FAMs.