Raman studies of nitrogen incorporation in GaAs_1-xN_x

We report direct-backscattering Raman studies of GaAs_1-xN_x alloys, for x≤0.03, grown on (001) GaAs. The Raman spectra exhibit a two-mode behavior. The allowed GaAs-like longitudinal-optic phonon near 292cm^-1 is found to red shift at a rate of -136±10cm^-1/x. This is well described by the combined effects of strain and alloying. The GaN-like phonon near 470cm^-1 is observed to increase in intensity in direct proportion to x, and to systematically blue shift at a rate of 197±10cm^-1/x. This blue shift is likewise attributed to strain and alloying. The GaAs-like second-order features are also seen to broaden slightly and diminish in intensity with increasing nitrogen concentration. These results are attributed to a weak breakdown in the zincblende-crystal long-range order, possibly related to the presence of ordered domains within the random alloy.