Importance of resonances in surface-electronic-state spectroscopy: (110) surfaces of ZnSe and ZnTe

The angle-resolved photoemission spectrum of the ZnSe(110) surface is reexamined, with several of its prominent features (in particular, the previously unexplained one near —4 eV) assigned to resonant one-electron surface states. The empty surface states observed in the electron-energy-loss spectra of ZnSe and ZnTe are interpreted as Zn 3d surface Frenkel excitonic resonances, caused by the final-state electron-hole interaction.