Vacancy-impurity complexes in highly n-type Si and SiGe: atomic structure, formation mechanisms, and electrical properties

K. Saarinen

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 [1]. The monovacancy surrounded by three As atoms is the dominant vacancy-impurity complex in Czochralski Si doped with As up to 1020 cm^-3 [1]. 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 [2]. 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 [3]. 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 [2]. 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 Si_0.96Ge_0.04 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 [4].

Reference:

[1] K. Saarinen, J. Nissilä, H. Kauppinen, M. Hakala, M. J. Puska, P. Hautojärvi, and C. Corbel, Phys. Rev. Lett. 82, 1883 (1999).
[2] V. Ranki, J. Nissilä, and K. Saarinen, Phys. Rev. Lett. 88, 105506 (2002).
[3] V. Ranki, K. Saarinen, J. Fage-Pedersen, J. Lundsgaard Hansen, and A. Nylandsted Larsen, Phys. Rev. B: Rapid Communications, in press (2003).
[4] S.-L. Sihto, J. Slotte, J. Lento, K. Saarinen, E. V. Monakhov, A. Yu Kuznetsov, and B. G. Svensson, Phys. Rev. B, submitted for publication (2003).