COMPARISON OF THERMALLY DETECTED OPTICAL-ABSORPTION AND ELECTROMODULATION SPECTRA OF GAAS ALGAAS QUANTUM-WELLS/

We report for the first time a comparative study of GaAs/AlGaAs quantu m well (QW) spectra obtained by thermally detected optical absorption (TD-OA) and photo- (PR) and electroreflectance (ER) experiments, respe ctively. The excitonic transition energies, obtained at low temperatur e with these methods, agree within 1 meV. It is demonstrated, using sa mples with different AlGaAs overlayer thicknesses, that the shape of t he TD-OA response is strongly influenced by interference effects for Q W's grown on absorbing substrates. A complete PR lineshape analysis yi elds phase angles for all transitions, whose differences can be attrib uted to the change of the AlGaAs front barrier thicknesses. ER investi gations following successive top layer removal confirm this interpreta tion.