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/${\mathrm{Ga}}_{0.7}$ ${\mathrm{Al}}_{0.3}$As quantum wells of widths scaling from 10 to 100 Å. In this experimental 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 than 50 Å we observe a decrease of the exciton binding energy and oscillator strength demonstrating the crossover from the two-dimensional to the three-dimensional behavior of excitons.