We present detailed analysis of inter- and intraband transitions in GaN/AlN self-organized quantum dots grown on sapphire, silicon (111) and 6H-SiC substrates. Samples containing quantum dots of different size were characterized by means of transmission electron microscopy, photoluminescence and photoinduced absorption spectroscopy. Interlevel transitions in the conduction band were identified in the 0.52-0.98 eV range covering the telecommunication wavelength band. The s-p(z), transition ranges from 0.52 eV to 0.8 eV for dots with height of 6 down to 1.5 nm, respectively. Experimental results are compared with theoretical calculations showing that in larger dots the transition energy is governed by the value of the internal field.