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

The transverse optical (TO) and longitudinal optical (LO) phonons of bulk (∼1-μm-thick) as-grown Ga_1-yIn_yAs_1-xN_x/GaAs [001] layers with x∼0.03-0.04 and y up to 0.30 are investigated by Raman scattering. Three-mode behaviour is observed which discriminates between Ga-N modes from isolated N atoms (∼460 cm^-1), clustered N in a Ga environment (∼425 cm^-1) and N involved in Ga₃InN complexes (∼480 cm^-1). The local N-bonding 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_s∼0.02 in GaAs.