Vacancy - phosphorus complexes in strained Si 1 À x Ge x : Structure and stability

We have used positron annihilation spectroscopy to study vacancy-type defects in strained phosphorus doped Si12xGex layers grown on Si substrates and irradiated with 2-MeV protons. The results show that the dominant defect in the SiGe layer after irradiation is the E center, the vacancy-phosphorus pair. When the sample is annealed at 150–175 °C, the dominant defect species in the SiGe layer changes into a complex consisting of a vacancy, a phosphorus dopant, and a germanium atom (V-P-Ge complex!. Furthermore, we observe that the total concentration of vacancy-type defect complexes before and after annealing remains approximately constant. We thus conclude that the V-P-Ge complex is formed when a migrating E center encounters a Ge atom and forms the V-P-Ge complex. The V-P-Ge complex anneals out at 200 °C. The 50 °C higher annealing temperature of the V-P-Ge complex corresponds to about 0.1–0.2 eV larger binding energy than that of the V-P pair. By ab initio calculations, we reproduce this value and confirm that the V-P pair is more stable when neighbored by a germanium atom.