Evolution of $E$-centers during the annealing of Sb-doped Si${}_{0.8}$Ge${}_{0.2}$

Evolution of the chemical surroundings of vacancy complexes in Sb-doped ($[\text{Sb}]=2\times {10}^{18}$ and $2\times {10}^{19}$ cm${}^{-3}$) Si${}_{0.8}$Ge${}_{0.2}$ was studied with positron annihilation spectroscopy in Doppler broadening mode. The study was performed by annealing the samples both isochronally and isothermally. Defect evolution was observed at the temperature range 450–650 K. Both treatments were shown to induce changes in the chemical surroundings of the $E$-centers via introduction of Ge near the defects. Moreover, Sb was found to hinder these changes by stabilizing the $E$-centers and thus preventing them from finding Ge. The stable state reached after the anneals was found to differ from that measured from an as-grown sample. This difference was deemed to be the result of Ge gathering in small clusters during the annealing thus breaking the initially random Ge distribution.

Figure 1

The low-momentum parameter $S$ (upper panel) and the high-momentum parameter $W$ (lower panel) as a function of annealing temperature in samples isochronally annealed at steps of 30 min. The values have been scaled to those of as-grown Si${}_{0.8}$Ge${}_{0.2}$. The typical error of the parameters is also indicated.

Figure 2

The ($S$,$W$) parameters measured in isochronally annealed Si${}_{0.8}$Ge${}_{0.2}$ samples. The data have been scaled to the values of as-grown Si${}_{0.8}$Ge${}_{0.2}$. Increasing symbol size represents increasing annealing temperature. The lines are drawn to guide the eye.

Figure 3

The ($S$,$W$) parameters measured in isothermally annealed Si${}_{0.8}$Ge${}_{0.2}$ samples. The data have been scaled to the values of as-grown Si${}_{0.8}$Ge${}_{0.2}$. Increasing symbol size represents increasing annealing time. The lines are drawn to guide the eye.

Figure 4

The momentum densities of as-grown and annealed Si${}_{0.8}$Ge${}_{0.2}$ samples along with theoretical calculations for $V$-Sb and $V$-Sb${}_2$ defects in Si. All densities have been scaled to that of bulk silicon. Samples 1 and 2 are as-irradiated ones with 2 $\times$ 10${}^{18}$ Sb/cm${}^{-3}$ and 2 $\times$ 10${}^{19}$ Sb/cm${}^{-3}$, respectively. Samples 3 and 4 are the same annealed isochronally at 800 K. Samples 5 and 6 have been isothermally annealed for 3 h at 550 K.

Figure 5

The evolution of $E$-centers in P- and Sb-doped Si and Si${}_{1-x}$Ge${}_x$ as a function of temperature in isochronal anneals. The highlighted areas show the temperature ranges for observing the defects shown within the highlight. Alongside each defect illustration, the evolution of positron parameters compared to the previous step in the process is shown with arrows. The half-red, half-green (two shades of gray) atom in the initial states indicates that in Si${}_{0.8}$Ge${}_{0.2}$ roughly half of the $E$-centers have at least one Ge atom as a nearest neighbor.