Résumé:

Microcalorimetric measurements of small absorption coefficients have been performed on thin GaN-AlGaN quantum wells grown by Reactive Molecular Beam Epitaxy on Al2O3 substrates. In addition to strong absorption at the energy of the GaN buffer 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 layers are combined with self consistent excitonic and envelope function calculations in the context of a model for the band line-ups which includes the piezoelectric effect. (C) 1999 Elsevier Science S.A. All rights reserved.