Raman Line-Shape Analysis of Random and Spontaneously Ordered GaInP2 Alloy

We have measured the temperature dependence of the Raman frequency and linewidth of the GaP-like LO phonon of random and spontaneously ordered GaInP2 alloys. The width of the asymmetric Raman band is strongly influenced by disorder and the anharmonicity of the lattice. The half-width towards the high-energy side of the Raman band of the GaP-like phonon is independent of temperature, while the half-width on the low-energy side does depend on temperature. Though no obvious differences are observed in the temperature dependence of the Raman spectra of the random and the ordered alloys, the GaP-like Raman band of the ordered samples narrows for incident photon energies near the fundamental gap of the alloy. We attribute the narrowing of the Raman band to the inhomogeneities in the material caused by the existence of a statistical distribution of partially ordered domains with different order parameters. From the observed width of the dispersion of the Raman linewidth as a function of incident photon energies under resonance conditions, it is concluded that samples grown at higher temperatures possess a narrower distribution of domains.