In this work, the band edge states of ZnS_1-xTe_x alloys grown by molecular beam epitaxy were studied using X-ray photoelectron spectroscopy (XPS) and photoluminescence excitation (PLE) techniques. Six ZnS_1-xTe_x samples with x values ranging from 2.5 to 100% are studied by XPS using monochromatized Al Kα( 1486.6eV) radiation. Their valence band XPS spectra are investigated and analyzed. The characteristics P_I and P_II valence band states were observed to shift to lower binding energy as Te composition increases. On the other hand, the valence band maximum in the photoemission spectra was found to move toward the Fermi level at higher Te composition. These observations are believed attributed to the mixture of ionic and covalent bonding in the alloy and the large difference in electronegati...[ Read more ]

In this work, the band edge states of ZnS_1-xTe_x alloys grown by molecular beam epitaxy were studied using X-ray photoelectron spectroscopy (XPS) and photoluminescence excitation (PLE) techniques. Six ZnS_1-xTe_x samples with x values ranging from 2.5 to 100% are studied by XPS using monochromatized Al Kα( 1486.6eV) radiation. Their valence band XPS spectra are investigated and analyzed. The characteristics P_I and P_II valence band states were observed to shift to lower binding energy as Te composition increases. On the other hand, the valence band maximum in the photoemission spectra was found to move toward the Fermi level at higher Te composition. These observations are believed attributed to the mixture of ionic and covalent bonding in the alloy and the large difference in electronegativity between S and Te atoms. Besides, two of the above ZnS_1-xTe_x samples with x = 2.5 and 8.6% were characterized by the PLE technique. The peak energy of the excitation spectrum is determined to be 3.59eV and 3.33eV for the alloy with x = 2.5 and 8.6% respectively, which are quite close to their corresponding band edge. The observed broadening in the transition below the band edge of the excitation bands is believed caused by direct excitation on the Te isoelectronic centers in this alloy system.