Exciton-polariton behaviour of the absorption edge of thin GaAs crystals with the "super-quantum" thickness and MQW enlarged barriers

At T = 1.7 K the optical absorption of pure GaAs samples with thickness d = 0.4 to 4.4 μm has been investigated in the region of the exciton-polariton resonances. The dependence of the integral absorption on the thickness is considered as a result of the competition of the optical processes in two different sample regions: near-surface region, where the integral absorption saturates due to increasing damping parameter in the electric field and central region, where the exciton-polariton is not perturbed. We have observed a series of narrow lines near the ground GaAs exciton state in the part of MQW spectra which belongs to the enlarged barrier. Calculations by the transfer matrix method give a good agreement with the model taking into account the quantization of the exciton as a whole and exciton-polariton wave interference.