Open-volume defect tails in Ge-implanted Si probed by slow positrons

Positron annihilation spectroscopy has been used in conjunction with anodic oxidation and etching to profile the distribution of open-volume defects beyond the range of 120 keV Ge ions implanted into (100) Si at a dose of 1×1014 cm−2. For a time-averaged dose rate (Jt) of 0.02 μA/cm−2 and incident angle of 7°, open-volume defects are found to exist at concentrations exceeding 1016 cm−3 at depths up to 600 nm, whereas the peak of the depth distribution of the implanted Ge ions (Rp) is 76 nm, measured using secondary ion mass spectroscopy. An increase in the depth of the defects observed when the implant is intentionally channeled on the 〈100〉 axis is thought to be simply correlated with a corresponding increase in Rp to 79 nm. When the time-averaged current is increased by a factor of 10 (incident angle=7°), defects persist at concentrations in excess of 1017 cm−3 beyond 1 μm and the Rp increases to 101 nm; this extended tail is attributed primarily to increased defect diffusion.