Surface core level shifts in III-V semiconductors: a high resolution photoemission study

We have performed photoemission experiments to determine the surface versus bulk contributions of In4d, Ga 3d and P 2p core level spectra in InP and GaP. The experiments were performed at the new VUV High Energy Resolution Photoemission beamline at the storage ring ELETTRA in Trieste. We obtained the values Delta E(In 4d)=-0.32 eV and Delta E(P 2p)=0.31 eV for the surface core level shifts of Indium and Phosphorous in InP(110), while the shifts for Ga 3d and P 2p in GaP(110) were -0.30 eV and 0.40 eV respectively. These results are discussed in terms of a simple model based on the difference between bulk and surface Madelung potentials.