Thermodynamics of free trions in mixed type GaAsAlAs quantum wells

Abstract An emission line which depends on the simultaneous presence of excitons and ∼10 10 cm −2 photoexcited electrons in a 20nm quantum well is shown to be due to free negatively charged excitons (“trions”). We have measured the temperature dependence of the exciton and trion lifetimes and of the exciton trion ratio, and demonstrate that the trion is a free particle analogous to the negative positronium ion. The binding energy is 1.3 meV and the lifetime is 1 4 of that of the exciton. Both lifetimes increase with temperature, as expected for a free particle. The intensity of the trion line relative to the exciton line is a good measure of the electron density.