Solid state light sources irradiating in the UV spectral region are key components in today technologies as they can replace conventional mercury vapor gas-discharge lamps. Ultrathin GaN layers in AlGaN barriers are of great interest for UV-emitting photonic devices, but a detailed understanding of the exciton features of these systems is still lacking. In this work, ultrathin GaN layers, grown by metal organic chemical vapour deposition, were deeply investigated in AlGaN barriers with different Al amount, in order to correlate excitonic effects with structural features.