We report a study of the luminescence properties of coherently strained GaAs1−xNx grown on GaAs by metalorganic molecular beam epitaxy. Well-defined photoluminescence was observed in samples with a nitrogen concentration up to 3%. Samples subjected to thermal anneals, investigated by x-ray diffraction and photoluminescence, show increased nitrogen incorporation and significant improvements in the luminescence efficiency. A band-gap reduction of more than 400 meV, compared to GaAs, is observed for a nitrogen concentration of ∼3%. For the range of nitrogen concentrations investigated here, the band gap follows predictions of the dielectric model of Van Vechten [J. A. Van Vechten and T. K. Bergstresser, Phys. Rev. B 1, 3351 (1970), and references therein].

Raman spectra of coherently strained layers of GaAs 1Ϫx N x grown on ͑001͒ GaAs with xϭ0 -0.05 by metalorganic molecular-beam epitaxy are reported. The optical phonons of the GaAs and GaN types, as well as disorder-activated acoustical phonons, are observed. A strongly confined GaAs optical mode at ϳ255 cm Ϫ1 , indicating the ordering of As and N atoms, is also detected. The GaAs-and GaN-type optical phonons exhibit strong diagonal components, forbidden for the zinc-blende structure. A bond polarizability analysis of the Raman selection rules shows that these components are activated by the trigonal distortion of the alloy lattice. The trigonal distortion arises from the formation of ordered ͕111͖-(GaN) m (GaAs) n clusters with nϭmϭ1.

We report direct-backscattering Raman studies of GaAs1−xNx alloys, for x⩽0.03, grown on (001) GaAs. The Raman spectra exhibit a two-mode behavior. The allowed GaAs-like longitudinal-optic phonon near 292 cm−1 is found to red shift at a rate of −136±10 cm−1/x. This is well described by the combined effects of strain and alloying. The GaN-like phonon near 470 cm−1 is observed to increase in intensity in direct proportion to x, and to systematically blue shift at a rate of 197±10 cm−1/x. This blue shift is likewise attributed to strain and alloying. The GaAs-like second-order features are also seen to broaden slightly and diminish in intensity with increasing nitrogen concentration. These results are attributed to a weak breakdown in the zincblende-crystal long-range order, possibly related to the presence of ordered domains within the random alloy.

We studied the photoluminescence from GaAsN/GaAs, with the nitrogen content of less than 0.5%. The low-temperature photoluminescence spectra are composed of several excitons bound to nitrogen complexes, each associated with different composition or configuration. These features were studied as a function of the excitation intensity, temperature, concentration, and growth conditions. The dependence of the binding energy of the dominant recombination center on the nitrogen concentration is interpreted in terms of a hierarchy of nitrogen complexes, from centers composed of at least two nitrogen atoms to more extended clusters. These excitonic transitions are very sensitive to growth parameters and can be used to study the statistical distribution of nitrogen in nominally uniform layers. We also show that the transition from nitrogen doping to alloy formation occurs for nitrogen concentrations above 0.25%.

High quality layers of GaAs1−xNx were grown on (001)GaAs by metal–organic molecular beam epitaxy. The growth conditions, and especially the nitrogen to arsenic flux ratio, were carefully explored to assure epitaxial crystal growth. We show well behaved and reproducible growth of single phase GaAs1−xNx with the GaN mole fraction as high as x=0.10. The nitrogen content of epitaxial layers was determined directly by secondary ion mass spectroscopy and high resolution x-ray diffraction.