Thickness dependence of photoluminescence excitation spectra of GaAs thin films due to confinement of excitonic polaritons

We demonstrated a remarkable thickness dependence of the absorption caused by polariton effect of exciton in GaAs thin films. Photoluminescence excita tion (PLE) spectra of high-quality GaAs films with thickness d = 80-160 nm at exciton resonance were measured at low temperature (5 K). Clear peaks fr om quantized center-of-mass motion of exciton confined in the GaAs layer we re successfully observed. We also confirm the nonlocal response of the quan tized states by the observed selection rules. The thickness dependence of t he absorption estimated by the PLE signal was in good agreement with the ca lculation results based on a transfer matrix method. These results indicate that the nonlocal response of the cofined states of exciton in the layer l eads to the enhancement of the internal field relevant to the confined mode of excitonic polariton. (C) 2000 Elsevier Science B.V. All rights reserved .