Preventing carbon contamination of Ge (001) during atomic layer deposition with a barium-based Zintl layer

Abstract

Carbon contamination of the clean Ge (001) 2 × 1 surface occurs during atomic layer deposition (ALD) of perovskite oxides and introduces impurities that can affect device performance. Zintl layers are formed by exposing a bare Ge (001) 2 × 1-reconstructed surface to 0.5-monolayers of elemental Ba, with the Ba atoms occupying the fourfold sites between Ge-dimer rows. The bare Ge (001) and Ba-Zintl layer surfaces feature a 2 × 1-reconstructed structure. Exposure of bare 2 × 1-reconstructed Ge (001) to 0.5 monolayers of elemental Sr leads to an 8 × 1- or 9 × 1-reconstructed Ge (001) surface. Bare Ge (001) and Ba-Zintl layer Ge (001), and 0.5-monolayer Sr-dosed Ge (001) surfaces were exposed to background molecules in the ALD chamber at 225 °C. Bare Ge (001) and Ba-Zintl layer Ge (001) were also exposed to barium bis(triisopropylcyclopentadienyl) at 225 °C and changes in the surface composition were monitored with x-ray photoelectron spectroscopy. The 2 × 1-reconstructed Ba-Zintl surface protects Ge (001) from carbon accumulation associated with ALD background molecules and cyclopentadienyl-based ligands originating from the ALD precursor. Surface structure is important in protecting Ge (001); the 8 × 1- or 9 × 1-reconstructed Ge (001) surface formed from 0.5-monolayers of Sr does not prevent carbon accumulation.