Two types of nitrogen plasma sources, an electron cyclotron resonance (ECR) plasma source and a radio frequency (rf) plasma source, were used for the growth of GaN by molecular beam epitaxy (MBE). GaN film quality was correlated with the optical emission characteristics of each type of nitrogen plasma source employed. The best quality GaN films were those grown using the rf nitrogen plasma source. This source was found to emit a much larger fraction of atomic nitrogen and 1st‐positive series excited molecular nitrogen in contrast to the ECR plasma source which mainly produced 2nd‐positive series excited molecular nitrogen and nitrogen molecular ions when operated under the same conditions. The benefit of homoepitaxial growth of GaN, using metalorganic vapor phase epitaxy grown GaN layers on basal plane 6H‐SiC, was seen by the observation of surface reconstructions before, during, and after GaN film growth by MBE. In addition, the MBE‐grown GaN films exhibited remarkably intense photoluminescence dominated by a sharp band‐edge peak at 3.409 eV having a full‐width at half‐maximum (FWHM) of 29.7 meV at room temperature. At lower temperatures, splitting of the near‐edge excition peaks was observed. Double‐crystal x‐ray rocking curve measurements of selected MBE‐grown GaN films yielded (0002) diffraction peaks having FWHMs as narrow as 156 arcsec.