Float zoning of high purity dislocation-free silicon was used to study the dependence of the minority carrier lifetime on various growth parameters and also as a means of growing heavily-doped p-type silicon of long life-time. We grew crystals doped with aluminum, boron, gallium and indium over a range of resistivities from 0.1 to 1000 ω cm and established correlations between lifetime and resistivity with the dopant species as a parameter. The effect of crystal cooling rate on lifetime was determined in the range 50 – 600 °C min −1 for both dislocated and dislocation-free crystals. A comparison of the influences of vacuum and gas ambients on calculated impurity distribution profiles was made for aluminum, antimony, arsenic, boron, copper, gallium, gold, indium, iron, manganese and phosphorus impurities in float-zoned and cold-crucible-grown silicon crystals. X-ray topography was used to examine dislocations, microdefects and process-induced damage.