Electronic properties and hyperfine parameters of gold-3d-transition-metal impurity pairs in silicon

We report theoretical investigations of the chemical trends in the electronic properties of transition-metal impurity pair complexes in a semiconductor. Self-consistent spin-unrestricted electronic state calculations, with a scalar relativistic scheme, in the framework of the multiple-scattering X alpha molecular cluster method, have been carried out for the substitutional gold-3d interstitial transition-metal pairs in silicon in C-3 upsilon Symmetry. The role played by the 5d and 3d states of the transition metals in the formation of the impurity energy levels in the crystal band gap and resonances is established. The analysis of the one-electron energy spectra of the AusTii, AusVi, AusCri, AusMni, AusFei, AusCoi, and AusNii pair impurities leads to the conclusion that the electronic, magnetic, and optical properties of the series can be explained by a simple microscopic model. The calculations do not provide support for the ionic model, where these pairs are described as two point charges electrostatically bounded with a strong magnetic coupling between their spins. Instead, the results lead to a model in which the covalent effects are invoked to explain the chemical trends and the physical properties of the complexes. This model is substantiated by comparing the hyperfine parameters and transition energies with electron paramagnetic resonance and optical experimental data.