We report on a solid-source B doping method for float-zone growth that uses nontoxic pyrolytic boron nitride as the source material and has the flexibility to allow step changes in doping concentration during the growth process. Doping concentrations of 6 x 10(16)cm(-3) or less (greater than or equal to 0. 3 Omega-cm resistivity) can be achieved in meter-long crystals without exceeding the solubility limit for N. Shorter crystals can be doped more heavily. The time required to transition from undoped (5000 Omega-cm) growth to a 0.2 Omega-cm uniform doping level is about 3 min. This corresponds to less than 1 cm of growth at 0.3cm min(-1). Doping uniformity is within 9% or better axially and 2% radially. We present and experimentally substantiate model equations for dopant incorporation from a pyrolytic BN solid-source, for B dopant dissipation when the source is removed, and for nitrogen co-dopant incorporation. (C) 2004 Elsevier B.V. All rights reserved.