Excited-State Trions in a Quantum Well

TL;DR

This study observes and characterizes an excited 2s state of a trion in a GaAs/AlGaAs quantum well using magneto-optical Kerr effect spectroscopy, revealing its magnetic field dependence and optical properties.

Contribution

First detection of the excited 2s trion state in a quantum well using MOKE spectroscopy, highlighting its magnetic field dependence and optical fingerprint.

Findings

2s trion appears below 2s exciton energy

2s trion is bound only above 1 T magnetic field

MOKE spectroscopy is crucial for detection

Abstract

We report on the observation of an excited 2s state of a trion in a 4.2 nm wide doped GaAs/Al(0.3)Ga(0.7)As quantum well (QW) using magneto-optical Kerr effect (MOKE) spectroscopy under out-of-plane magnetic fields up to 6 T. This resonance appears slightly below the 2s exciton in energy. Strikingly, the 2s trion is found to be bound only for magnetic fields larger than 1 T. The signature of the 2s trion is absent in the magneto-reflectance spectra, while it is detectable in the MOKE spectra signifying the importance of the powerful technique. Similar to the 1s states, the 2s 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 2s excited trion.