Determination of excitonic properties in GaAs/Ga_1-xAl_xAs quantum wells by optical waveguiding experiments

The absorption of single GaAs quantum wells in Ga1-xAlxAs or GaAs/AlAs short-period superlattices is studied in optical waveguiding experiments at low and at room temperatures. The authors show that a complete characterization and determination of the guide parameters is essential in order to determine accurately the optical properties of quantum wells or superlattices embedded in the guide. The waveguiding configuration allows one to obtain the quantum well absolute absorption coefficients in both polarization directions, parallel and perpendicular to the plane of the layers, and to determine the exciton binding energies and the associated oscillator strengths. New results are presented for an enlarged quantum well in a superlattice. The authors show that the excitonic binding energies depend on the extension of the wavefunction in the superlattice and are different for heavy- and light-hole excitons. The experimental values obtained for a quantum well in an alloy agree well with recent theoretical calculations.