Positron diffusion in Si

Positron diffusion in Si(100) and Si(111) has been studied using a variable-energy positron beam. The positron diffusion coefficient is found to be $D_{+}$=2.7±0.3 ${\mathrm{cm}}^2$/sec using a Makhov-type positron implantation profile, which is demonstrated to fit the data more reliably than the more commonly applied exponential profile. The diffusion-related parameter, $E_0$, which results from the exponential profile, is found to be 4.2±0.2 keV, significantly longer than previously reported values. A drastic reduction in $E_0$ is found after annealing the sample at 1300 K, showing that previously reported low values of $E_0$ are probably associated with the thermal history of the sample. Reconstruction of the Si(111) into the 7×7 (low-energy electron diffraction) structure had no detectable effect on the positron diffusion behavior.