First-principles study of Ge dangling bonds with different oxygen backbonds at Ge/GeO_2 interface

摘要

Calculations based on the density functional theory predict the formation of gap states near the Ge conduction-band minimum, due to the presence of the dangling bonds of Ge~(1+) and Ge~(2+) atoms at the Ge/GeO_2 interface. Additionally, gap states near the valence-band maximum appear in the presence of threefold Ge~(0+) dangling bonds at the Ge/GeO_2 interface. To further discuss the electrical property of the GeO_2 near the interface, the oxygen-vacancy-related defect in GeO_2 is calculated with bulk oxide structure. The result shows that the thermodynamical-transition level of +2/0 is 5.11 eV above the valence-band maximum of GeO_2. The high transition level energy indicates the +2 charge state is a possible source for positive fixed-charges in defective GeO_2.