Excited-State Trions in a Quantum Well

Abstract

We report on the observation of an excited 2⁢𝑠 state of a trion in a 4.2 nm wide doped GaAs/Al0.3⁢Ga0.7⁢As quantum well using magneto-optical Kerr effect (MOKE) spectroscopy under out-of-plane magnetic fields up to 6 T. This resonance appears slightly below the 2⁢𝑠 exciton in energy. Strikingly, the 2⁢𝑠 trion is found to be bound only for magnetic fields larger than 1 T. The signature of the 2⁢𝑠 trion is absent in the magnetoreflectance spectra, while it is detectable in the MOKE spectra signifying the importance of the powerful technique. Similar to the 1⁢𝑠 states, the 2⁢𝑠 trion shows an opposite degree of magnetic-field-induced polarization compared to its exciton counterpart, in agreement with our theoretical calculations. This transfer of oscillator strength between the complexes establishes an optical fingerprint of the 2⁢𝑠 excited trion.