We report our observations on the homoepitaxial diamond growth by microwave plasma emical vapor deposition (MPCVD) experiments on Type Ib diamond substrates conducted by varying three independent variables. In a feed gas mixture of H2, N2, O2, and 13CH4, the amount of nitrogen was varied in the range of 0 to 4000 ppm, the amount of methane was varied from 2% CH4/H2 to 6% CH4/H2, and the substrate temperature was varied in the range of 850 to 1200 °C. We used isotopically enriched carbon-13 methane gas as the source of carbon in the plasma to clearly distinguish the grown diamond layer from the underlying substrate using Raman spectroscopy. The x-ray rocking curve measurements confirmed the homoepitaxial nature of the deposited layers with a slight increase in the full width at half-maximum for sample grown with the highest nitrogen content in the plasma. Optical and atomic force microscopy revealed dramatic changes in surface morphology with variation in each parameter. The nitrogen incorporation in carbon-13 diamond layers was monitored through photoluminescence spectroscopy of nitrogen-vacancy complexes. A twentyfold increase in diamond growth rate was clearly achieved in this multivariable study. © 2009 Materials Research Society.