Résumé
Microcalorimetric measurements of small absorption coefficients have been performed on thin GaN–AlGaN quantum wellsgrown by Reactive Molecular Beam Epitaxy on Al 2O 3 substrates. In addition to strong absorption at the energy of the GaNbuffer and at the energy of the thick AlGaN barrier layers, we could also readily detect transitions associated to the quantum well.These measurements which pave the way to a precise determination of the gap mismatch between the well and the barrier layersare combined with self consistent excitonic and envelope function calculations in the context of a model for the band line-upswhich includes the piezoelectric effect.