Nitrogen in Float-Zoned silicon is electrically inactive in as-grown state, but upon annealing, numerous deep centres are generated In the past. only selected annealing temperatures were tried In the present study a wide temperature range was inspected The effect of anneal was sensitive to the cooling rate With slow cooling following anneals, the room-temperature hole concentration (in boron-doped samples with an initial resistivity of 1200 Ohm cm) was almost unchanged. The temperature dependence of the hole concentration (monitored by resistivity and Hall effect) showed however that various deep donors were generated Depending on the anneal (and oil the cooling rate), levels at 0 36, 0 3, 0 2 or 0 1 eV (above the top of the valence band) were found These levels are assigned to the vacancy-nitrogen species VN(5,) VN(7), VN(9) and VN(11), respectively. (C) 2009 Elsevier B.V. All rights reserved