uv Photoemission Measurements of the Upper<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>d</mml:mi></mml:math>Levels in the IIB-VIA Compounds

Abstract

Photoemission measurements have been made of the upper $d$ levels in ZnO, ZnSe, ZnTe, CdS, CdSe, CdTe, HgSe, and HgTe using 21.2-eV (584-\AA{}) and 16.8-eV (740-\AA{}) radiation. All the samples except for HgSe and HgTe were cleaved and measured in an oil-free ion-pumped vacuum system at a pressure in the ${10}^{\ensuremath{-}7}$-${10}^{\ensuremath{-}8}$ Torr range. The results agree extremely well with values obtained by x-ray-induced-electron-emission spectroscopy. The spectra obtained for HgSe and HgTe make it possible to positively verify the identification of certain peaks observed in photoemission spectra of the IIB-VIA compounds as being due to the upper $d$ levels. The photoemission results reported in this study are also compared with both reflectivity and energy-loss measurements to obtain information about the optical density of states in the conduction bands of these compounds.