Binding energies of positive and negative trions: From quantum wells to quantum dots

We compare binding energies for positive and negative trions in a series of narrow GaAs quantum wells and in "natural" quantum dots defined by quantum well thickness fluctuations. We assign photoluminescence features to oppositely charged trions through a combination of charging behavior, luminescence polarization, and spin fine structure. Negative trions are found to have a higher binding energy than positive trions. Our observations compare well with path integral Monte Carlo calculations for different well widths. This comparison provides a physical interpretation of the observed trends and sheds light on a longstanding disagreement between theory and experiment on the influence of lateral confinement on trion binding energies.