Protons at the Si-SiO2 interface: a first principle investigation

We studied protons attached to bridging O atoms in the vicinity of the Si(1 0 0)-SiO₂ interface through density-functional calculations for realistic interface models. These protons do not disrupt the bonding network except in the case of strained Si-O bonds for which they lead to the formation of positively charged threefold coordinated Si(3)⁺. Defect energies mainly fall within a band of ∼0.5 eV, which is stabilized by ∼0.3 eV at the interface, the energies of the Si(3)⁺ defects lying at the bottom of this band. Hence, this work indicates that bridging O atoms in the vicinity of the interface can act as shallow proton traps and describes a mechanism for bond-rearrangements leading to Si(3)⁺. These results are consistent with experimental observations.