Investigation of electric fields in B-implanted Si by positron beam spectroscopy

Besides its conventional applications in defect characterization, variable-energy positron annihilation spectroscopy can be employed to monitor internal electric fields in the depletion regions in semiconductor structures. In this work, electric fields were studied in pre-amorphized Cz Si wafers (background dopant level ∼ 1015 cm–3) implanted with 0.5 keV B ions at a dose of 1015 cm–2, and then annealed isothermally at 800oC for times ranging from 1 to 2700 s. Differences in the S parameter with annealing time were observed in samples implanted (a) with B ions only and (b) with B followed by F ions at 10keV; these were attributed to different electric fields, which drift positrons back (a) to the surface, or (b) to a vacancy-like defected layer. Fitting of the data revealed depletion regions of widths between 150-350 nm centered at depths between 250-350 nm, with electric field values in the range -9 x 106 to -3 x 106 Vm–1. The depth and width of the depletion regions increase significantly for annealing times greater than 100 s, attributed to B diffusion. The results are consistent with simple theoretical estimates, but the uncertainties on the latter are large