EPR INVESTIGATION OF PT- IN SILICON

Using EPR we have resolved the question of whether the dominant Pt- defect in silicon consists of an isolated platinum ion or a platinum-platinum pair. We have measured the uniaxial-stress-induced shifts in the g values and find that the stress-coupling tensor shows the defect symmetry to be C2-upsilon. By selective doping with Pt-195 and Pt-198, we demonstrate that there is no hyperfine evidence of a second platinum. We therefore conclude that the original model of Woodbury and Ludwig of an isolated substitutional platinum impurity that spontaneously distorts off center in a <100> direction is correct. We have also measured the defect realignment under stress, which occurs even at pumped-liquid-helium temperatures. We find that the sense of the alignment for this platinum defect is opposite to that for the negative vacancy. In addition, we have fully resolved the superhyperfine interaction involving the two nearest-neighbor silicon atoms. Lastly, we observe a shift in the g values depending upon the nuclear isotopes of these two nearest-neighbor silicon atoms.