Nanocrystalline sp²-BN thin films have been grown on (0001) 4H-SiC substrates at 1030 °C via continuous flow and discontinuous flow-modulated chemical vapor deposition techniques using diborane (B₂H₆) and ammonia (NH₃) as the B and N sources, respectively. The latter technique enabled observations of both the effect of hydrogen purge steps between precursor injections and the length of injection times for B₂H₆ on the stoichiometry and microstructure of the films. Stoichiometric BN was achieved in all films grown continuously within the N/B gas phase ratio range of 20–200; this was not observed for the discontinuously grown films unless both the B₂H₆ flow rate and the injection time were minimized. Cross-sectional transmission electron microscopy of films grown both continuously and discontinuously at N/B = 200 and using short B₂H₆ injection times relative to that of NH₃ for the latter process route revealed the initial growth of ∼4 nm thick partially ordered sp²-BN layers. A transition zone then formed containing randomly oriented polycrystalline grains. Excess B incorporated into the discontinuously grown films during long B₂H₆ injection times resulted in single layer mixtures of amorphous and sp²-BN without any observed ordering.