Properties of iron-doped multicrystalline silicon grown by the float-zone technique

Multicrystalline Fe-doped Si ingots were float-zoned from high-purity feed rods. Fe was introduced by pill-doping, which gives uniform impurity content for small segregation coefficients (k/spl sim/10/sup 15/ for Fe in Si). Fe concentrations were calculated from the initial weight of the Fe pill, the molten zone geometry and the growth parameters. Values in the range of 10/sup 12/-10/sup 16/ atoms/cm/sup 3/ were targeted. No additional electrically active dopants were introduced. Minority charge carrier lifetime (via YAG-laser-excited, 430 MHz ultra-high-frequency-coupled, photoconductive decay) was measured on the ingots, and wafers were cut to examine grain structure and electron-beam-induced current response of grain boundaries. Observed lifetimes decreased monotonically with increasing Fe content for similar grain sizes (from /spl sim/10 /spl mu/s to 2 /spl mu/s for <10/sup -3/ cm/sup 2/ grains, from /spl sim/30 us to 2 us for /spl sim/5/spl times/10/sup -3/ cm/sup 2/ grains, and from /spl sim/300 /spl mu/s to 2 us for >10/sup -2/ cm/sup 2/ grains) as the Fe content increased to 1/spl times/10/sup 16/.