Evidence of a replacement reaction between ion implanted substitutional Tl dopants and interstitial Si atoms

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Abstract
The lattice location of implanted Tl atoms in Si has been studied by means of the channeling technique. A motion from substitutional sites into the tetrahedral interstitial sites along the 〈111〉 rows is observed under carbon bombardment at temperatures around 300 °C. It is concluded, that this motion is due to an indirect process associated with the carbon bombardment. We suggest that Si interstitial atoms created during bombardment diffuse to substitutional Tl atoms and displace them into interstitial sites in a Watkins type replacement reaction. A strong temperature dependence is observed, and the process appears to be thermally activated. No effect is detectable (i) for a room temperature bombardment or (ii) for a 340 °C bombardment of a Tl implant that contains a majority of implanted substitutional As dopants. The lattice location of implanted Tl atoms depends markedly on implantation temperature and dose but for the temperature region used in earlier studies (350450 °C) there is nearly a 1:1 relation between substitutional and interstitial fractions.