We have investigated nitrogen incorporation mechanisms in dilute nitride GaAsN alloys grown by plasma-assisted molecular-beam epitaxy. A comparison of nuclear reaction analysis and Rutherford backscattering spectrometry in channeling and nonchanneling conditions reveals significant composition-dependent incorporation of N into nonsubstitutional sites, presumably as either N -N or N -As split interstitials. Furthermore, we identify the ͑2 ϫ 1͒ reconstruction as the surface structure which leads to the highest substitutional N incorporation, likely due to the high number of group V sites per unit area available for N -As surface exchange.

Inelastic proton scattering at forward angles has been carried out on ' 0 and "0 at a bombarding energy of 201 MeV. The (p, p') spin-flip transitions to I+ and 2 states are compared with (e, e'), (p, y), and charge exchange data, and with microscopic distorted-wave Born approximation calculations using shell model wave functions. The ratios of orbital to spin contributions are deduced for the known 1+ states in ' O.with entrance and exit windows made of thin Kapton (C22HtpN204)" foils. In contrast to the case of solid targets which are, in general, 10 -20 pm thick, the relatively large length of the gas cell along the beam axis (of the or-35 1201

We have investigated the evolution of structural and optical properties of GaAsN nanostructures synthesized by N ion implantation into epitaxial GaAs, followed by rapid thermal annealing. Transmission electron microscopy and x-ray diffraction indicate the formation of nanometer-sized crystallites with lattice parameters close to those of pure zincblende GaN. The average crystallite size increases with annealing temperature while the size distribution is self-similar and the volume fraction remains constant, suggesting a coarsening process governed by Ostwald ripening. These GaAsN nanostructures exhibit significant photoluminescence in the near infrared range. The apparent lowering of the fundamental band gap is likely due to the incorporation of a small amount of As in GaN.

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