Splitting of the local mode frequency of substitutional nitrogen in (Ga, In)(As, N) alloys due to symmetry lowering

Fourier transform infrared absorption measurements have been carried out on nitrogen-implanted InyGa1-yAs layers grown by molecular beam epitaxy. After rapid thermal annealing in the temperature range of 700-900 degrees C local vibrational mode absorption due to substitutional nitrogen (N-As) is detected. Different configurations of the nearest-neighbour shell are identified by the associated shift of the local mode frequency. With increasing indium content in the epitaxial layer, the formation of indium-rich environments is observed, more pronounced than is expected for a random distribution of the constituents. The influence of resonance interactions with lattice phonon bands on intensity and line shape of local modes is discussed. The comparison with calculations based on a valence force model gives a consistent picture of substitutional nitrogen bonding in the different configurations. The dominant effect is the strengthening of the nitrogen-gallium bond whenever a further indium atom is incorporated in the nearest-neighbour shell of nitrogen.