Several novel features are observed in the low‐temperature photoluminescence spectra of AlxGa1−xAs layers grown on GaAs by metalorganic chemical vapor deposition. GaAs substrate luminescence spectra are observed through AlxGa1−xAs layers as thick as 22 &mgr;m. Both carrier diffusion to the substrate and AlxGa1−xAs luminescence are identified as the excitation mechanisms of the GaAs luminescence, and a minority‐carrier diffusion length of 10 &mgr;m is estimated. The presence of photon recycling in the AlxGa1−xAs layers is demonstrated by comparison of photoluminescence (PL) spectra for layers with and without GaAs substrates, as well as PL examination of two AlxGa1−xAs heterostructures.