This dissertation investigates the effect of n-type doping on the optical spectra of the dilute nitride GaAsN alloy system. Using conventional and high spatial resolution photoluminescence (PL), including the temperature and power dependence, photoreflectance and time-resolved photoluminescence measurements together with structural characterizations (X-ray diffraction and transmission electron microscopy) we identify the effect of local modulation doping of band-tail states in these alloys. I use the modeling of nitrogen composition distribution over large supercells to further demonstrate the existance of intrinsic phase separation arising from the disorder nature in these dilute nitride alloys. This model allows us to explain several debated issues, like the existence of quantum dots and the additional splitting of the photoreflection spectra, in a self-consistent way. I also use frequency-domain and time-domain simulation methods to calculate optical mode structures in III-V semiconductor microcavities with self-assembled quantum dots as light source. Our future work includes the design of Whispering-Gallery mode (WGM) laser devices using the dilute nitrides.