The role of La surface chemistry in the passivation of Ge

The oxidation of a Ge surface by molecular oxygen in the presence of ultrathin La, Al, and Hf layers was examined by in situ x-ray photoelectron spectroscopy. Upon exposure to O-2, clean bare Ge and Hf-covered or Al-covered Ge surfaces show no Ge-O bond formation. On the contrary, a La-covered Ge surface strongly reacts with O-2 forming a stable germanate LaGeOx compound. This has a beneficial side effect for the interface because the formation of volatile GeO is suppressed, resulting in the good passivating properties of LaGeOx. The photoemission results are correlated with the oxygen density differences in the corresponding oxides.