Well-resolved higher excited states of the light- and heavy-hole free excitons in a 225-Å ${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As-GaAs multi-quantum-well structure

Several excited states of the light- and heavy-hole free excitons have been observed in a 225-Å ${\mathrm{Al}}_{0.35}$ ${\mathrm{Ga}}_{0.65}$As-GaAs multi-quantum-well (MQW) structure using photoluminescence excitation spectroscopy. The 2s and 3s states of both the heavy-hole free exciton, as well as of the light-hole free exciton, were identified. The measured values of the difference in energy between the ground state 1s and the 2s state of both the heavy-hole and the light-hole free excitons agree with their calculated values. The binding energy of the 3s state is estimated using a hydrogen model, and the differences in energy between the 1s state and the 3s state of both the heavy-hole and the light-hole free excitons thus obtained are compared with their measured values. Magnetic field measurements were also made to verify the transition assignments.