The presence of a bismuth surfactant is found to increase the nitrogen incorporation in the dilute nitride GaNxAs1-x by as much as 60% during growth by molecular beam epitaxy. Films with nitrogen concentrations in the 0.4-0.95% range were grown using an RF plasma source for nitrogen. The Bi surface coverage is inferred from reflection high-energy electron diffraction as a function of Bi flux and substrate temperature, and the nitrogen content is obtained by high-resolution X-ray diffraction. At constant substrate temperature the nitrogen content is found to increase with Bi coverage, which has the form of a Langmuir isotherm when plotted as a function of Bi flux. (c) 2005 Elsevier B.V. All rights reserved.