Influence of strain on the Al incorporation in AlxGa1-xN films grown on different underlayers and the properties of AlxGa1-xN/GaN two-dimensional (2D) heterostructures were investigated. The Al-containing III-nitride films and heterostructures were grown on (0 0 0 1) sapphire substrates by metalorganic chemical vapor deposition using alternate supply of group III metalorganics and ammonia (NH3). It appears that the incorporation of Al in the AlxGa1-xN films from gas phase is greatly affected by the biaxial strain in the AlxGa1-xN films depending on the mismatch status between the grown AlxGa1-xN film and its underlayer. In some cases, huge mismatch between AlxGa1-xN film and the underlayer tends to result in a compositional separation in the AlxGa1-xN film. Photoluminescence (PL) measurements of Al0.08Ga0.92N/GaN SQW structures and absorption measurements of Al0.5Ga0.5N/GaN SLSs and AlN/GaN SLSs reveal the same tendency of decrement in PL emission energies and reduction in absorption cut-off energies as the GaN well width in SQW and SLS increases, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.