We study the growth of InAs/AlxGa1-xAs/GaAs heterostructures as well as their structural and optical properties. Structurally coherent InAs islands with a narrow size distribution are found to be formed only in a very narrow range of InAs coverage. In striking contrast, the photoluminescence band in the 1.15–1.35 eV spectral range, which is commonly attributed to the emission from InAs quantum dots, is present for all of our structures, regardless the presence or absence of InAs islands and their strain state. Moreover, for constant InAs coverage this PL band follows not the Γ gap but the L gap of the AlxGa1-xAs barrier. This latter result is in disagreement with effective mass calculations for three-dimensionally confined excitons.