Percolation-based multimode Ga-N behaviour in the Raman spectra of GaInAsN

The transverse optical (TO) and longitudinal optical (LO) phonons of bulk (~1-(mu)m-thick) as-grown Ga/sub 1-y/In/sub y/As/sub 1-x/N/sub x//GaAs [001] layers with x~0.03-0.04 and y up to 0.30 are investigated by Raman scattering. Threemode behaviour is observed which discriminates between Ga-N modes from isolated N atoms (~460 cm/sup -1/), clustered N in a Ga environment (~425 cm/sup -1/) and N involved in Ga/sub 3/InN complexes (~480 cm/sup -1/). The local Nbonding in GaInAsN is quantitatively estimated via full contour modelling of the TO multimode Ga-N Raman lineshapes. In particular, it is found that the incorporation of In can significantly reduce GaN segregation, but only for a very narrow range of N compositions just above the theoretical N-solubility limit x/sub s/~0.02 in GaAs.