We report on the effects of N incorporation on the electronic properties of (InGa)(AsN)/GaAs heterostructures as investigated by photoluminescence (PL) spectroscopy. PL under a magnetic field shows an increase in the electron effective mass in the N-containing material. In order to address this effect as well as the giant band gap reduction induced by N in (InGa)As, we exploit the ability of hydrogen to passivate the electronic activity of N in (InGa)(AsN). Such passivation is due to the formation of N-H bonds and manifests itself as: (i) a quenching of the exciton recombination in N-related complexes in the N dilute limit; (ii) a blueshift of the (InGa)(AsN) band gap toward that of the N-free material in the alloy limit. A thermal annealing leads to a complete recovery of the electronic properties (InGa)(AsN) had before H irradiation in both limits. The activation energy for the thermal dissociation, E-D, of the N-H complexes follows a Gaussian distribution with a mean value increasing with the N concentration, y. Values of E-D similar to those found in the alloy limit are found in the case of very dilute N concentrations (impurity limit), where different N-H complexes are singled out. These results show that different N complexes are responsible for the puzzling effects exerted by N on the electronic properties of (InGa)(AsN). (C) 2002 Elsevier Science Ltd. All rights reserved.