Vacancy-model interpretation of EPR spectrum of Si:Pt−

The vacancy model for platinum in silicon as proposed by Watkins postulates a neutral Pt atom in the 5${\mathit{d}}^{10}$ electronic configuration occupying a negatively charged lattice vacancy, so that electronic properties of ${\mathrm{Pt}}^{\mathrm{-}}$ should be similar to those of the isolated vacancy ${\mathit{V}}^{\mathrm{-}}$. We show that this model, including strong Pt spin-orbit coupling and a Jahn-Teller (JT) distortion of ${\mathit{C}}_{2\mathit{v}}$ symmetry combining tetragonal and trigonal components, and having only ∼10% of the electronic wave function localized on the Pt, is qualitatively consistent with the results of the electron-paramagnetic-resonance (EPR) studies of Woodbury and Ludwig, which revealed an unusual form for the g tensor (nearly axial about 〈100〉 but departing strongly from the spin-only value of 2, with ${\mathit{g}}_{\mathrm{\perp }}$<2<${\mathit{g}}_{\mathrm{\parallel }}$). The model accounts also for the anisotropic Pt hyperfine interaction and for superhyperfine interaction found to involve only two of the four nearest-neighbor Si atoms. With three electrons in ${\mathit{t}}_2$ vacancylike orbitals the JT distortion has two energetically similar forms yielding the same ${\mathit{C}}_{2\mathit{v}}$ symmetry, one of which occurs for ${\mathit{V}}^{\mathrm{-}}$ and the other for ${\mathrm{Pt}}^{\mathrm{-}}$. With this identification, opposite signs found for the experimental strain-coupling coefficients of ${\mathit{V}}^{\mathrm{-}}$ and ${\mathrm{Pt}}^{\mathrm{-}}$ may be explained. The vacancy model predicts a positive value for the product ${\mathit{g}}_{\mathit{x}\mathit{x}}$ ${\mathit{g}}_{\mathit{y}\mathit{y}}$ ${\mathit{g}}_{\mathit{z}\mathit{z}}$, the opposite of that given by an alternative model due to Ammerlaan and van Oosten, which predicts ∼70% localization in the Pt 5d shell. These models can, therefore, be distinguished by an experiment that determines this sign.