SULFUR L(2,3) AND ZINC M(2,3) SOFT-X-RAY FLUORESCENCE-SPECTRA IN CDS AND ZNS

The sulfur L(2,3) Soft-x-ray emission spectra of wurtzite CdS and cubi c ZnS and the zinc M(2,3) spectra of ZnS have been measured using both photon and electron-beam excitation. The photon-excited sulfur L spec tra are found to be much sharper than electron-beam-excited spectra. U sing photon excitation between the L(2) and L(3) thresholds, a pure L( 3) spectrum-is obtained for both materials. Broad features of the S L spectra, consisting of a lower valence band (LVB) derived from the sul fur 3s orbital and an upper valence band (UVB)derived from S 3p and Cd (Zn) s and p orbitals, are typical of materials with mixed ionic-coval ent character. A narrow band between the UVB and LVB is associated wit h overlap of Zn 3d and Cd 4d orbitals onto the S site. The s+d local p artial density of states derived from these spectra provide a rigorous test of band-structure calculations; they are in good agreement for t he position, width, and structure of the LVB and UVB, but place the d band deeper in the subband gap than theory predicts. The Zn M(2,3) spe ctrum has large lifetime broadening and thus provides limited informat ion. However, near-threshold excitation of this spectrum shows dramati c effects resulting from an electronic resonance Raman process.