We report on the growth and structural characterization of GaN/GaAs/GaN structures prepared on (0 0 0 1) sapphire substrates by rf-plasma-assisted molecular beam epitaxy. A well-confined As-rich layer was obtained for the sample in situ annealed at 700 degreesC in between the growth of the GaN cap layer and the GaAs. From the transmission electron microscopy analysis, it is found that the formation of intrinsic stacking faults is associated with the high As concentration present in the layer. The asymmetry of the As profile obtained by secondary ion mass spectrometry indicates As surface segregation during the GaN cap layer growth. (C) 2002 Elsevier Science Ltd. All rights reserved.