Electronic structure of defect centers P1, P2, and P4 in P-doped SiO2

We have studied the ground-state properties of phosphorus-related dia- and paramagnetic point defects in P-doped silica and alpha -quartz. Density functional theory calculations have been performed to determine the structure, charge and spin distribution of the P1, P2, and P4 centers. P1 consists of a three-coordinated P atom substituting for a Si atom in the SiO2 lattice, [(O-)(3)P-.](+), in radical form; P2 denotes a four-coordinated P, [(O-)(2)P-.(-O)(2)](0); P4 has only two P-O bonds, [(O-)(2)P-.](0). These centers originate from electron or hole trapping derived from diamagnetic precursors. The computed hyperfine coupling matrices of the paramagnetic centers fully confirm the proposed assignment of the P1, P2 and P4 structures to the observed EPR signals in P-doped silica and P2 in alpha -quartz.