AlN/GaN layered structures with layer periods between 1.5 and 40 nm have been grown on (0001) oriented sapphire and α(6H)‐SiC substrates. The growth was performed using a modified gas source molecular‐beam epitaxy (MBE) technique. Standard effusion cells were used as sources of Al and Ga, and a small, MBE compatible, electron cyclotron resonance (ECR) plasma source was used to activate nitrogen gas prior to deposition. Chemical analysis of the layers was conducted using Auger spectrometry. X‐ray diffractometry, transmission electron microscopy (TEM), and high‐resolution electron microscopy (HREM) were employed for the structural and microstructural studies. Coherent interfaces (no relaxation by misfit dislocations) were observed for bilayer periods smaller than 6 nm. By contrast, completely relaxed individual layers of GaN and AlN with respect to each other were present for bilayer periods above 20 nm. Cathodoluminescence showed a shift in the emission peak from 3.42 eV for the sample with individual 10‐n...