A study of polar CdTe (111) surfaces using angle-resolved x-ray photoelectron and Auger electron spectroscopy and low-energy electron diffraction

Abstract

X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and low-energy electron diffraction (LEED) have been used to study the polar (111)Cd and (111)Te surfaces of intrinsic CdTe crystals. Complementary information on surface composition, chemical state of the surface elements, and surface structure was obtained. The Auger parameters were used to identify the chemical states of elements on surfaces of semi-insulating undoped CdTe crystals which suffered from static charging effects. With this approach, we were able to determine that after chem-mechanical polishing, the Te-rich surface layer was mostly in the pure Te state. Only a trace amount of TeO2 was detectable. Sputtered and vacuum annealed (111) surfaces were found to be stoichiometric: both Cd and Te were in the chemical state of CdTe. Both (111) Cd and (111) Te surfaces showed sixfold symmetric LEED patterns. No evidence of surface reconstruction was found. Angle-resolved XPS showed no significant difference between 0° and 70° tilt on either the (111) Cd or (111) Te surfaces. Angle-resolved AES, however, showed significant differences between (111) Cd and (111) Te at 0° and 70° tilt, and the crystallographic polarity identified this way was consistent with results based on chemical etching and standard AES techniques, and with reported results of x-ray diffraction and transmission electron microscopy.