Dangling bond defects at Si-SiO₂ interfaces: Atomic structure of the P_b1 center

Using a first-principles approach, we characterize dangling bond defects at Si-SiO₂ interfaces by calculating hyperfine parameters for several relaxed structures. Interface models, in which defect Si atoms remain close to crystalline sites of the substrate upon relaxation, successfully describe P_b and P_b0 defects at (111) and (100) interfaces, respectively. On the basis of calculated hyperfine parameters, we discard models of the P_b1 defect containing a first neighbor shell with an O atom or a strained bond. A novel model consisting of an asymmetrically oxidized dimer yields hyperfine parameters in excellent agreement with experiment and is proposed as the structure of the P_b1 center.