Abstract The influence of important growth parameters upon the shape of the solid-liquid interfaces of the floating zone, and the macroscopic radial dopant distribution of phosphorus-doped, dislocation-free silicon single crystals is investigated. Qualitative preliminary models for the modelling of the melt shape by several growth parameters are presented. General conclusions on single growth parameters are not possible because of the strong interdependence of all parameters. Radial dopant inhomogeneities of up to 40% were found even for -crystals grown under suitable conditions. This implies that also growth mechanisms other than facet growth play an important role for the radial dopant distribution. For  crystals, radial dopant inhomogeneities of up to 70% have been found because of the additional effect of facet growth. Facets alone lead to a radial variation of about 30%. For  growth, facetting can be avoided by a proper choice of the growth parameters. Their suitable combination enables the crystal grower to obtain crystals with reasonably even dopant profiles, although the reproducibility is not too good.