Semiempirical electronic-structure calculations of hydrogen-phosphorus-vacancy complexes in crystalline silicon

Abstract

The author reports on self-consistent calculations for the electronic structure of three hydrogen-phosphorus-vacancy complexes in crystalline silicon, based on a semiempirical tight-binding theory. These complexes, denoted by V-1H-3P, V-2H-2P, and V-3H-1P, consist of a vacancy and substitutional phosphorus impurities on the nearest-neighbour sites of the vacancy. The remaining silicon dangling bonds in the complexes are all saturated by hydrogen atoms. Each of the complexes is described by a large repeated supercell and the authors use the recursion method for computing local densities of states and orbital electron occupancies. They find that the three complexes do not introduce energy levels into the fundamental band gap, revealing that the electrical activity of the silicon dangling bonds can be well passivated by hydrogen atoms at bonding positions through strong orbital interactions and by phosphorus atoms at substitutional positions through Coulomb attractions. However, the complexes can have defect resonant states outside of the band gap. The authors show that these resonant states can be well described in terms of the symmetric combinations of the phosphorus orbitals and the symmetric combinations of the hydrogen and the hydrogen-saturated silicon orbitals.