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/sub +/ = 2.7 +- 0.3 cm2/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, E0, 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 E0 is found after annealing the sample at 1300 K, showing that previously reported low values of E0 are probably associated with the thermal history of the sample. Reconstruction of the Si(111) into the 7 x 7 (low-energy electron diffraction) structure had no detectable effect on the positron diffusion behavior