Electron Emission Studies of the IIB-VIA Semiconductor Compounds

X-ray induced electron emission measurements were used to determine the energy levels of core electrons in ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, HgS, HgSe and HgTe. The investigated energy range extends from the bottom of the valence band (6-8 eV below the Fermi level) to about 1200 eV below the Fermi level. Chemical shifts were determined by comparing the results of these measurements with experimental values for the pure elements. These shifts are plotted as a function of the fractional ionicity values determined by Phillips and Van Vechten, Pauling and Coulson. Core level values for ZnSe and CdTe are compared with self-consistent relativistic orthogonalized plane wave calculations for the excitation energies of these compounds. Agreement with these theoretical calculations is best for the levels closest to the valence band and appears to be angular-momentum dependent. For the first time, spin-orbit splitting values were experimentally determined for several levels including Zn 3d, Cd 4d and Hg 5d levels. The measured energy values for the upper d-levels are compared with values obtained by ultraviolet induced electron emission, ultraviolet reflectivity and electron energy loss measurements. (Author)