Observation of Polaritons in GaAs: A New Interpretation of the Free-Exciton Reflectance and Luminescence

Abstract

The reflectance and luminescence of high-purity epitaxial layers of GaAs have been studied at low temperatures. Strong polariton and spatial dispersion effects are seen for the $n=1$ free exciton. The longitudinal-exciton energy is found to be 1.5151\ifmmode\pm\else\textpm\fi{}0.0001 eV (at 2 K) and the transverse-exciton energy is quite near 1.5149 eV. Two luminescence structures at 1.5154 and 1.5148 eV are identified with radiative decay from the upper and lower polariton branches, respectively.