BINDING-ENERGIES AND OSCILLATOR-STRENGTHS OF EXCITONS IN THIN GAAS GA0.7AL0.3AS QUANTUM-WELLS/

We report experimental results of optical-absorption experiments in a waveguiding geometry at low temperature in thin GaAs/Ga0.7Al0.3As quan tum wells of widths scaling from 10 to 100 Angstrom. In this experimen tal configuration, the single quantum-well absorption coefficients are obtained in both polarization directions, parallel and normal to the plane of layers. The binding energy and oscillator strength of the 1s heavy and light excitons are determined. For well thicknesses less tha n 50 Angstrom we observe a decrease of the exciton binding energy and oscillator strength demonstrating the crossover from the two-dimension al to the three-dimensional behavior of excitons.