Auger electron spectroscopy (AES) and electron energy loss spectroscopy (EELS) studies of GaP and Si surfaces

Abstract

We report an AES and EELS analysis of the title semiconductors, the main emphasis being placed on highlighting surface chemical change as a function of exposure to the atmosphere, electron irradiation and Ar + ion etching. By comparison with the corresponding atomically clean surfaces obtained by UHV cleavage, the ambient-induced oxidation/contamination film covering the two materials can be quantitatively characterized by AES, which also provides fair chemical-state information on the species formed. We find that GaP develops a P x O y -rich layer in the more external regions (∼0.4 nm), whereas the chemistry of the inner regions (∼2–3 nm) is comparatively less affected. Electron irradiation affects the surface chemistry of atomically clean GaP to a much greater extent than that of Si. Indeed, short (3 h) irradiation is already sufficient to “deposit” sizable amounts of oxidic and carbonaceous species, which spread coherently over the whole GaP surface, as testified in EELS spectra by the disappearance of the surface plasmon signal characteristic of this semiconductor. Conversely, no appreciable chemical change is observed in both AES and EELS spectra of Si for durations ⩽24 h. The Si notch surface is covered with a SiO 2-like film which can be removed for the most part by Ar + etching. The surface left after this treatment is meaningfully less C- and O-rich than that obtained after exposing the cleaved material to the atmosphere for a few seconds. The Ar + etched silicon surface also shows the Si 0-related surface plasmon signal, and the intensity ratio between this signal and the companion bulk plasmon signal is systematically lower than the corresponding value from the atomically clean surface in the kinetic energy range 300–2000 eV. The difference between the ratios from the two materials is particularly high in low-KE spectra, an evidence which is tentatively interpreted as arising from Ar +-roughening phenomena occurring in the etched surface, as opposed to the comparatively flat cleaved surface. These results add further evidence to a comparative appraisal of the diagnostic capabilities of Auger and EELS spectra in surface science studies of semiconductors.