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 5d10 electronic configuration occupying a negatively charged lattice vacancy, so that electron properties of Pt- should be similar to those of the isolated vacancy V-. We show that this model, including strong Pt spin-orbit coupling and a Jahn-Teller (JT) distortion of C2-upsilon symmetry combining tetragonal and trigonal components, and having only approximately 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 g perpendicular-to < 2 < g parallel-to). 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 t2 vacancylike orbitals the JT distortion has two energetically similar forms yielding the same C2-upsilon symmetry, one of which occurs for V- and the other for Pt-. With this identification, opposite signs found for the experimental strain-coupling coefficients of V- and Pt- may be explained. The vacancy model predicts a positive value for the product g(xx)g(yy)g(zz), the opposite of that given by an alternative model due to Ammerlaan and van Oosten, which predicts approximately 70% localization in the Pt 5d shell. These models can, therefore, be distinguished by an experiment that determines this sign.