Saturation of light- and heavy-hole exciton energies in very narrow quantum wells

We report the experimental observation of a decrease in the difference in the energies of the ground-state light- and heavy-hole excitons as the widths of single $\frac{\mathrm{GaAs}}{{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}}$ quantum wells become very narrow. This is a consequence of the saturation of ground-state exciton energies at a value equal to that of excitons in the barrier material. Although this effect is well known theoretically, this is the first clear experimental evidence of a phenomenon which is an additional manifestation of the quantum-mechanical nature of the properties of the structure.