Raman scattering probe of anharmonic effects due to temperature and compositional disorder in GaNxAs1−x

Abstract

Using micro-Raman spectroscopy, we have investigated the vibrational properties of coherently strained GaNxAs1−x alloys grown on GaAs (001) substrates by molecular beam epitaxy. The effect of compositional disorder in GaNxAs1−x alloys has been studied by analyzing the broadening, asymmetry, and line shift of the first-order LO mode and nitrogen-induced localized vibration mode (NLVM). It is found that the line shape and peak shift of GaAs-like LO mode in GaNxAs1−x can be well described by the spatial correlation model. We have also analyzed Raman spectra of GaNxAs1−x alloys in the temperature range of 80–500K. The intensity of GaAs-like LO phonon and NLVM decreases with temperature and the linewidth of both these modes shows substantial broadening at higher temperature. The temperature dependence of phonon linewidth and peak frequency of LO modes are analyzed in terms of anharmonic damping effect induced by thermal and compositional disorders. We have observed that the anharmonicity in GaNxAs1−x is higher than that in GaAs, and increases with the N content in GaNxAs1−x alloys. In addition, both thermal and compositional disorder-induced anharmonicities lead to an appreciable change of the LO phonon lifetime. These results obtained from Raman investigations would lead to a better understanding of the anharmonic effects in dilute nitrides.