Defect Tails in GE Implanted Si Probed by Slow Positrons and Ion Channeling

Positron annihilation spectroscopy has been used to profile the distribution of defects following implantation of 120keV Ge+ into (100) Si in the dose range l x 1010 - 1x104 cm-2. The openvolume defect profiles can be adequately fitted assuming a simple rectangular block distribution extending to 350nm. Using anodic oxidation and etching, a procedure is described which allows details of the defect tails beyond the range of the implanted ion, usually inaccessible to positron -2 annihilation measurements, to be determined. For a time averaged dose-rate (Jt) of 0.02µA cm-2 and incident angle of 7°, open-volume defects are found to exist at concentrations exceeding 1016cm-3 at depths upto 600nm whereas the peak of the depth distribution of the implanted ions (Rp) is 76nm, measured using SIMS. When the time-average dose-rate is increased by a factor of 10, defects persist at concentrations in excess of 1017cm-3 beyond lµm and the Rp increases to 101nm. The open-volume defect profiles are compared to those deduced from Rutherford backscattering-channeling using the fitting routine DICADA.