Vacancy-impurity complexes in highly n-type Si and SiGe: atomic structure, formation mechanisms, and electrical properties
Laboratory of Physics, Helsinki University of Technology, P. O. Box 1100, 02015 HUT, Finland
The detailed atomic structure of vacancy-impurity complexes in highly n-type Si or SiGe can be experimentally determined by combining positron lifetime and electron momentum density measurements . The monovacancy surrounded by three As atoms is the dominant vacancy-impurity complex in Czochralski Si doped with As up to 1020 cm-3 . By studying the annealing of V-As pairs formed by electron irradiation, we can show that the V-As3 complexes are formed as a result of the subsequent migrations of V-As and V-As2 . The V-As3 complexes are dominant defects also in highly As-doped MBE grown Si, where they exist at concentrations relevant to the electrical deactivation of doping . Larger complexes, identified as V2-As5, are also present at high concentrations. The V-As3 and as V2-As5 defects are removed by annealings at 800 and 900 °C, respectively. However, they are likely to reconstruct during the cooling down by migrations of V-As and V-As2, as demonstrated in electron irradiated material . The rapid thermal annealing is shown to lead to smallest concentrations of V-As3 and as V2-As5, most likely due to the limited time available for the migration processes.
In P-doped strained Si0.96Ge0.04 layers grown on Si the vacancy-phosphorus pair is identified as the dominant vacancy defect after 2 MeV proton irradiation at room temperature. After annealing at 150 °C the V-P pairs convert to V-P-Ge complexes consisting of a vacancy surrounded by P and Ge atoms. We conclude that the V-P-Ge complex is formed when a migrating V-P pair encounters a Ge atom. The V-P-Ge complex anneals at 200 °C, corresponding to about 0.1 - 0.2 eV higher binding energy than that of the V-P pair. By ab-initio calculations we reproduce this value and conclude that the V-P pair in SiGe becomes more stable when neighbored by a Ge atom .
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