We report on the further investigation of the fundamental properties of GaAsN compounds and GaAs/GaAsN/InGaAs heterostructures grown by MBE. The strain-induced splitting of light-hole and heavy-hole bands of tensilly strained GaAsN is observed. The presented dependence of the band gap in unstrained GaAsN on the nitrogen content differs substantially from the one predicted by the theory (IEEE J. Sel. Topics Quantum Electron. 3 (1997) 719) assuming that the band gap in GaAsN can be reduced to zero. The space-indirect transition between hole localized in InGaAs and electron localized in GaAsN is detected. The value of the valence band discontinuity between GaAs and GaAsN0.02 at 18 K was evaluated to be 15 +/- 5 meV taking into account the band gap of GaAsN alloy. Band-edge lineup in heterostuctures with GaAsN layer is determined from experimental data. (C) 2002 Elsevier Science B.V. All rights reserved.