Inverse exciton spin orientation due to trion formation in modulation doped quantum wells

TL;DR

This study investigates how trion formation in doped quantum wells causes inverse exciton spin orientation, revealing a rapid trion formation process and potential for electric field-based spin control.

Contribution

It demonstrates that spin-dependent trion formation leads to inverse exciton spin polarization in doped quantum wells, a novel insight into spin manipulation mechanisms.

Findings

Inverse exciton spin orientation observed in doped samples.

Trion formation time measured as 2 ps, shorter than exciton-photon interaction time.

Effective depletion of Zeeman sublevels explains inverse polarization.

Abstract

Time-resolved and time-integrated circularly polarized photoluminescence of excitons and trions in external magnetic fields up to 10 T has been studied in undoped and n-type doped quantum well structures based on ZnSe. In an undoped structure, a circular polarization of photoluminescence induced by magnetic fields corresponded to the Boltzmann distribution of excitons on Zeeman sublevels. The inverse spin orientation of excitons is observed in doped samples with a carrier density of $3 \times 10^{10}$ cm$^{-2}$ and higher. Model calculations show that the reason for the inverse spin orientation is the effective depletion of the lowest-exciton Zeeman sublevel as a result of the spin-dependent formation of trions. The trion formation time as a result of exciton-electron binding was determined as 2 ps. This is noticeably shorter than the characteristic time of the exciton-photon interaction. The observed effect can be considered as a way of spin manipulation by electric fields.