Oxidation of Ge(100) and Ge(111) surfaces: an UPS and XPS study

Abstract In situ and ex situ oxidation studies are carried out on Ge(100) and Ge(111) employing techniques of ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS). In situ oxidation produces mainly GeO on both the surfaces. Ge 3d and 2p levels show a chemical shift of about 1.4 and 1.8 eV respectively corresponding to this oxide. GeO desorbs from the surface on annealing to 400°C without undergoing any transformation. On exposing to air, a mixture of oxides consisting mainly of GeO and GeO 2 are formed on both the surfaces. Ge 3d and 2p levels show a chemical shift of 3.2 eV for GeO 2 . The amount of GeO 2 increases with increasing time of exposure to air. The spectral features of both the species have been identified by UPS and XPS. GeO 2 can be selectively removed from the surface by rinsing the sample in warm water. Atomically clean surfaces of Ge have been achieved by thermally decomposing a thin oxide layer prepared ex situ by chemical means, similar to Ishizaka and Shiraki's method for Si. O 1s and O 2p spectra of SiO and GeO species exhibit distinctly different binding energy values and this helps unambiguous assignment of the bonding partner.

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