In situ X-ray photoelectron spectroscopy study of the oxidation of CuGaSe 2

Abstract

The thermal and native oxidation of CuGaSe 2 thin films was studied by in situ X-ray photoelectron spectroscopy (XPS). The special design of the XPS chamber allowed to measure XP-spectra under oxidizing gas atmospheres at pressures of up to 5 mbar (in situ) or in ultra high vacuum (UHV). During thermal oxidation, the formation of predominantly Ga 2O 3 and some amount of SeO 2 were observed, but no copper oxides could be detected in the near surface region of the thin films. The same oxides were found after native oxidation in air under ambient conditions. Only after long term native oxidation for longer than 4 months Cu(OH) 2 was detected. An additional sodium oxide compound formed at the thin film surface, Na x O and Na 2CO 3 after thermal and native oxidation, respectively. The amount of these sodium oxide compounds depends on the Na content on the as prepared surface. The formation of SeO 2 under humid conditions at 100 °C was found to depend on the surface composition of the thin film.