XPS study of fresh and oxidized GeTe and (Ge,Sn) Te surface

The energies of Ge 2p(3/2), Ge 3d, Te 3d(5/2), Te 4d(5/2) and Sn 3d(5/2) ph otopeaks were measured for vacuum-cleaved GeTe and Ge0.9Sn0.1Te crystals, o btained by the 'vapour-solid liquid' technique (VLS). The oxidation of clea ved surfaces in air at ambient temperature and humidity was studied by X-ra y photoelectron spectroscopy (XPS). The oxidation seems to take place even after few minutes of air exposure. The first stage of the oxidation results in entire Ge oxidation to the oxidation state 4 + and partial Te oxidation to the elemental state. The intermediate oxidation product is supposed to he GeO2-xTex. The second stage is slower than the first one, and it leads t o further Te oxidation to 4 + oxidation state and also the significant surf ace enrichment in Ge. (C) 2001 Elsevier Science B.V. All rights reserved.