Surface photovoltage effects onp-GaAs (100) from core-level photoelectron spectroscopy using synchrotron radiation and a laser

The surface photovoltage (SPV) effect on laser-excited p-GaAs (100) has been investigated using core-level photoelectron spectroscopy with synchrotron radiation (SR). The energy shift of the Ga3d photoelectrons due to the SPV effect was remarkably dependent on the sample temperature and the laser photon flux. The dependence in each case was well interpreted on the basis of a simple SPV formula derived from the band-bending scheme with excess photocarriers. The magnitude of the band bending was about 0.8 eV for clean p-GaAs (100) surfaces having no electrodes. Similar core-level shifts were observed in the Ga3d and Cs4d spectra of Cs/GaAs (100), indicating an unpinned behavior of the electronic states of the Cs surface layer. The time response of the SPV effect was also investigated in the nanosecond range using a pump-probe method with SR and the laser.