Experimental band structure of cadmium sulfide

We have investigated the bulk electronic structure of wurtzite CdS using angle-resolved photoelectron spectroscopy with synchrotron radiation. We find that direct transitions largely determine the shape of the experimental spectra. Information from all high-symmetry points in the Brillouin zone is available from normal- and off-normal-emission spectra with the aid of polarization selection rules. A comparison with our experimentally determined critical-point energies shows that existing theoretical band-structure calculations for wurtzite CdS are qualitatively correct, but underestimate the extent of the band dispersion. For example, we observe an upper-valence-band width of 4.5 eV, which is significantly larger than the predicted values of 2.7—3.3 eV. Our spectra also reveal fine structure in the Cd $4d$ core-level spectra. This suggests that the Cd $4d$ electrons are involved in the chemical bonding.