Quaternary GalnAsN containing a small amount of nitrogen (<2%) is a potentially promising material for realizing long-wavelength emission lasers for applications in optical communication systems. Such devices should have better high-temperature characteristics than conventional InGaAsP lasers due to an increase of the conduction band offset. In this thesis, the GS-MBE growth of quaternary GalnAsN and ternary GaAsN was carried out. Active N was produced by passing high purity nitrogen gas into either an RF or an ECR plasma source. The RF plasma source was found to produce better quality nitrides. Characterization techniques such as photoluminescence, X-ray diffraction, TEM, SIMS, and Hall effect measurements were used to characterize thick layers (e.g. 1 pm) and quantum wells of these nitride materials. The concentration of N incorporated into GalnAs and GaAs is very dependent on growth conditions and plasma conditions. The incorporation of a small amount of N into compressively strained InGaAs reduces the strain and produces a red-shift of photoluminescence peak. However, compared to N-free InGaAs materials, the optical quality is dramatically degraded yielding reduced photoluminescence intensity and a broadened FWHM of the PL peak. Hall effect measurements on un-doped, Si-doped, Bedoped thick GalnAsN layers indicate the presence of a high concentration of electron and hole traps. The results of SIMS suggest that impurity H might be responsible for the deep level defects formed. However, the nature of the defects is currently unknown. From TEM observations and comparison to samples grown with a He-plasma instead of a Nplasma, spinodal decomposition and ion-induced damage in GalnAsN may produce the reduced quality of materials, but these are not the major reasons responsible for the dramatic degradation of optical quality. Thermal annealing was found to be an effective method for significantly improving the optical quality of GalnAsN with a low N concentration. Optimum annealing conditions were obtained. Hall effect measurements on annealed samples indicate that electron and hole traps are reduced but still present after anneal. / Thesis / Master of Engineering (ME)