High magnetic field spin splitting of excitons in asymmetric GaAs quantum wells

Abstract

Low-temperature photoluminescence from high-quality GaAs quantum wells, asymmetrically doped with carbon, are investigated under high magnetic fields (up to 20 T) directed along the [001] growth axis. At higher fields, in the ${\ensuremath{\sigma}}^{\ensuremath{-}}$ polarized emission, we observe two well-resolved lines which are attributed to the recombination of neutral ($X$) and charged ($X$${}^{+}$) excitons. In contrast, only the neutral exciton line is observed for the ${\ensuremath{\sigma}}^{+}$ polarization. From the difference of the $X$ line positions for the two polarizations we determine the effective Zeeman splitting of neutral excitons and then the $g$ factor g${}_{h}$ of confined holes. We find that g${}_{h}$ depends substantially on the well size and changes the sign at moderate magnetic fields. To explain the experimental results, the valence Landau levels are calculated using the Luttinger model beyond the axial approximation. We demonstrate that mainly the excited hole levels contribute to the excitonic state at higher magnetic fields. Due to their light-hole character, resulting from the valence-band mixing, the excited hole states have a sizable overlap with the electron states confined far from the doped barrier. The calculated values of g${}_{h}$ are in an excellent quantitative agreement with the experimental data.