Monolayer Passivation of Ge(100) Surface via Nitridation and Oxidation

Abstract

The monolayer passivation of Ge(100) surface via formation of Ge-N and Ge-O surface species was studied using scanning tunneling microscopy (STM) and density functional theory (DFT). Direct niridation using an electron cyclotron resonance (ECR) plasma source formed an ordered Ge-N structure on a Ge(100) surface at 500oC. DFT calculation found the hydrogen passivation on this Ge-N ordered structure could reduce the bandgap states by decreasing the dangling bonds and the bond strain. Oxidation of Ge(100) using H2O produced an -OH and -H terminated surface with very few Ge ad-atoms, while e-beam evaporation of GeO2 formed semi-ordered Ge-O structures and Ge ad-species at room temperature. Annealing above 300oC formed suboxide rows on both H2O and GeO2 dosed surfaces, and the scanning tunneling spectroscopy (STS) showed that the Fermi level was pinned near the valence band edge on the n-type Ge surfaces covered by suboxides.