Line width resonance of the longitudinal optical phonon in GaAs:N

We extend resonant Raman scattering studies of Mascarenhas et al. [PRB68, 233201 (2003)] of GaAs$_{1-x}$N$_x$ to the ultra-dilute nitrogen doping concentrations, whereby we unambiguously resolve the line width resonances of the LO phonon. A discontinuity is observed in the LO phonon line width resonance energy as a function of concentration. With decreasing nitrogen concentration the $E_W$ line width resonance energy reduces by ca. 40 meV at $x=0.4\%$. This value corresponds to the concentration, at which the localized to delocalized transition manifests itself in the electro-reflectance signature line widths.