Comparison between experimental and theoretical determination of the local structure of the GaAsN dilute nitride alloy

We present a combined experimental and theoretical study of the local structure of a dilute nitride alloy, GaAs$_{1-y}$N$_y$. Experimental results obtained by X-ray Absorption Spectroscopy have been compared with first-principles density-functional supercell calculations and with the predictions of different Valence Force Field models. Both experiments and calculations find that inclusion of N induces static disorder in the Ga-As bond length distribution. An increase in the Ga-As bond length with N concentration is found; this is due to the competing effects of the decrease of the free lattice parameter and of tensile strain due to pseudomorphic growth. A good agreement between the experimental and theoretical determination of the bond length expansion is found. We discuss the performance of the Valence Force Field models in predicting the bond length expansion.