Photoreflectance versus ellipsometry investigation of GaAs/Al0.3Ga0.7As MQW's

In this communication we report on experimental results obtained from the combined use of ellipsometry and photoreflectance to investigate the optical response of typical MQW structures. The motivation for this approach is related to the need for a correct analysis of the lineshape of photoreflectance spectra. Ellipsometric data yield two important contributions about the nature and the degree of localization of the spectral structures in the excitonic region: (a) experimental curves instead of model profiles as starting reflectivity functions for derivations, (b) possible values of oscillator strengths of the transitions investigated. The energies of the main spectral features are compared with the quantized electronic levels obtained in the framework of the effective mass approximation in the envelope function scheme and a discussion of data previously reported in the literature is performed with the help of results obtained by the coupled techniques.