Picosecond electro-optic sampling of electron-hole vertical transport in surface space charge fields

The longitudinal electro-optic effect in GaAs(100) is used to measure the dynamics of electron-hole pair separation in surface space charge fields present at GaAs/oxide interfaces. At low photocarrier injection, the rise time in the E field transient is a direct measurement of the charge transport across the space charge field which is found to be faster than 500 fs. The results demonstrate that the charge carriers are energetically unthermalized at the surface prior to the surface chemistry. This method is also found to be sensitive to 10−5 of a monolayer of charged surface states.