Monovacancy and Interstitial Migration in Ion-Implanted Silicon

The migration of monovacancies ($V^0$) and self-interstitials ($I$) has been observed in ion-implanted low-doped float-zone silicon by variable-energy positron annihilation spectroscopy. $V^0$ and $I$ were created by the in situ implantation of $\sim 20\mathrm{keV}$ helium ions below 50 K. Monitoring the time evolution of the vacancy response during isothermal heating enabled the measurement of activation energies for $V^0$ and $I$ migration of 0.078(7) and 0.46(28) eV, respectively. In highly As-doped Si, partial $V$ annihilation occurs via free $I$ migration, with a second stage of annealing, probably associated with $V$-As complexes, above room temperature.

Figure 1

Schematic diagram of sample chamber.

Figure 2

$S$ parameter vs incident positron energy for FZ Si at 25 K, before and after irradiation with $\sim 20\mathrm{keV}$ He ions, and after annealing at 300 K. The solid lines are fits to the data.

Figure 3

Percentage difference between the $S$ parameter for implanted FZ Si (measured at an incident positron energy of 3.5 keV) and its asymptotic value at times $>3d$ as a function of time at 220 and 300 K.

Figure 4

As for Fig. 3, for $n^{+}\mathrm{Si}$ at 263 and 337 K.

Figure 5

Arrhenius plots of $\ln {\lambda }_S$ vs $1000/T$, where ${\lambda }_S$ is the decay constant resulting from exponential fits of data such as those in Figs. 3, 4, and $T$ is the absolute temperature in K.