Vacancy-Impurity Complexes in Highly Sb-Doped Si Grown by Molecular Beam Epitaxy

Positron annihilation measurements, supported by first-principles electron-structure calculations, identify vacancies and vacancy clusters decorated by 1–2 dopant impurities in highly Sb-doped Si. The concentration of vacancy defects increases with Sb doping and contributes significantly to the electrical compensation. Annealings at low temperatures of 400–500 K convert the defects to larger complexes where the open volume is neighbored by 2–3 Sb atoms. This behavior is attributed to the migration of vacancy-Sb pairs and demonstrates at atomic level the metastability of the material grown by epitaxy at low temperature.

Figure 1

$S$ parameter vs positron implantation energy, converted to the mean stopping depth in the top axis. The $S$ parameter is scaled to the bulk lattice value $S_B$ obtained in the substrate. The inset shows the results in samples with the native oxide on the surface.

Figure 2

The momentum density along the [111] direction at the irradiation-induced $V-\mathrm{Sb}$ and $V-{\mathrm{Sb}}_2$ defects, as scaled to that of the $V-\mathrm{P}$ pair. The lines are obtained from theoretical calculations, showing also the influence of lattice relaxation (fraction of the Si-Si bond length, Sb atoms relaxed only).

Figure 3

Momentum density of the vacancy defect in the as-grown Sb-doped Si (sample No. 2) and after annealing at 575 K. The measured momentum density along the [100] direction is scaled to that of the $V-\mathrm{P}$ pair along the [111] axis, leading to oscillations. The lines in the upper panel are obtained from theoretical calculations in various model structures.

Figure 4

$S$ and $W$ parameters (measured at 300 K, positron energy 1 keV, sample No. 2) vs annealing temperature. The parameters are scaled to their lattice values $S_B$ and $W_B$.