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We report on observation of photoluminescence in 1.2-1.4 eV spectral range from As-doped GaN layers grown by plasma-assisted molecular beam epitaxy. We attribute this emission to recombination in GaAs inclusions formed during the growth process in the GaN(As) layers. This near-infrared emission is efficient under UV photoexcitation, but its intensity is low for excitation energies below the band gap of GaN. Low-temperature photoluminescence spectra reveal a set of sharp emission lines with maxima from 1.516 eV to 1.436 eV. We attribute some of these sharp lines to the emission of excitons bound to nitrogen incorporated into the GaAs crystallites and also to their GaAs-like optical phonon replicas. Photoluminescence excitation spectra show a series of maxima, which can be attributed to the formation of bound and free excitons and also to the formation of excitons with the simultaneous emission of GaAs-like optical phonons.

We have investigated the influence of an additional bismuth flux during growth on the properties of GaN films prepared by plasma-assisted molecular beam epitaxy. A wide range of bismuth fluxes have been used, at the highest Bi flux this was larger than the flux of Ga. X-ray and photoluminescence studies demonstrate that the structural quality and optical properties of the GaN films grown at $800 C are practically unchanged. X-ray and Auger studies indicated that the concentration of Bi in the bulk of the films grown at $800 C is rather small. We have demonstrated that it is possible to grow conductive metallic Bi films epitaxially onto GaN films in-situ after epitaxy by reducing the deposition temperature. Bismuth may thus potentially be a new material for in-situ contacts to GaN layers and device structures.

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