Angle-resolved x-ray photoelectron spectroscopy study of GeO_x growth by plasma post-oxidation

The growth process of GeO_x films formed by plasma post-oxidation (PPO) at room temperature (RT) is investigated using angle-resolved x-ray photoelectron spectroscopy (AR-XPS). The experimental results show that the distributions of the Ge⁴⁺ states, a mixture of the Ge²⁺ and Ge³⁺ states, and the Ge¹⁺ states are localized from the GeO_x surface to the GeO_x/Ge interface. Moreover, the Ge¹⁺ states are predominant when the two outermost layers of Ge atoms are oxidized. These findings are helpful for establishing in-depth knowledge of the growth mechanism of the GeO_x layer and valuable for the optimization of Ge-based gate stacks for future complementary metal-oxide-semiconductor (MOS) field-effect transistor (CMOSFET) devices.