Internal transitions of neutral and charged magneto-excitons in GaAs/AlGaAs quantum wells

We have used Optically Detected Resonance (ODR) spectroscopy to probe the e lectronic properties of undoped and barrier-doped GaAs/Al0.3Ga0.7As multipl e-quantum-well (MQW) samples with well widths between 12.5 and 20 nm in mag netic fields up to 15 T at low temperatures. The simultaneous observation o f electron and hole CR along with several internal transitions of neutral e xcitons (IETs) verifies the symmetry-related energy differences of the inte rnal transitions to differences between electron and hole CR. The observed degeneracy of the 1s --> 2p(+) IET from the two radiative magneto-excitons is due to the very small electron g-factor. ODR measurements on 20 nm wide MQWs (not-intentionally- and barrier-doped) exhibit transitions of the nega tively charged excitonic complex.