Diamond films have been grown by hot filament and microwave plasma assisted CVD using precursor gas mixtures of 1% methane in hydrogen with additional nitrogen and boron dopants. Structural and compositional characterisation of the as-grown films was carried out by scanning electron microscopy and secondary ion mass spectrometry. SIMS measurements show the B-doping efficiency is close to unity, whereas that of nitrogen is less than 10(-3). In conjunction with modelling of the gas-phase CVD environment we show that variations in the film morphology and quality can be accounted for by changes in the concentrations of the gas-phase precursor species rather than incorporation of the dopant into the diamond lattice.