A new silicon phosphide, Si₁₂P₅: Formation conditions, structure, and properties

The formation conditions, structure, and properties of the recently discovered phosphide, Si₁₂P₅ (initially assigned Si₇P₃), have been studied using x-ray diffraction, high-resolution transmission electron microscopy, photospectrometry, and a four-point probe. The phosphide formed in amorphous Si–P alloy thin films with 30, 35 and 44 at. % P after annealing at 1000 °C for 30 min. During annealing at 1100 °C, the phosphide dissociated through P evaporation. The Si₁₂P₅ phase is proposed to have rhombohedral symmetry with a P3̄1m space group and a C₅W₁₂ structure. The hexagonal lattice parameters measured were a=6.16±0.05 Å and c=13.17±0.01 Å. The optical band gap and the electrical resistivity of the phosphide were determined to be 1.55 eV and 5 mΩ cm, respectively. The Gibbs free energy diagram for the Si–P system was modified to include this new Si₁₂P₅ phase.