SURFACE SHG AND PHOTOEMISSION FROM CS P-GAAS AND THE CS/O-2/P-GAAS COADSORBED SYSTEM/

We have made simultaneous measurements of the optical second harmonic generation (SHG) intensity and the photoemission current from the p-ty pe GaAs (100) (p congruent to 2 x 10(19) cm(-3)) surface covered by Cs alone and the same surface covered by both Cs and O. The photoemissio n current was monitored simultaneously with the SH intensity as a func tion of the adsorbate coverage. We found a clearly negative correlatio n between the SH intensity and the photoemission current on both the C s/p-GaAs system and the Cs/O/p-GaAs coadsorbed system. The physical or igin of this correlation is discussed in relation to the transformatio n of surface electronic states with coverage of Cs and O.