Circular polarization of excitonic luminescence in CdTe quantum wells with excess electrons of different densities

Abstract

The circular polarization of excitonic luminescence is studied in $\mathrm{CdTe}/{\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Mg}}_{x}\mathrm{Te}$ quantum wells with excess electrons of low density in an external magnetic field. It is observed that the circular polarization of X and ${X}^{\ensuremath{-}}$ emissions has opposite signs and is influenced by the excess electron density. If the electron density is relatively high so that the emission intensity of the negatively charged excitons ${X}^{\ensuremath{-}}$ is much stronger than that of the neutral excitons X, a stronger circular polarization degree of both X and ${X}^{\ensuremath{-}}$ emissions is observed. We find that the circular polarization of both ${X}^{\ensuremath{-}}$ and X emissions is caused by the spin polarization of the excess electrons due to the electron-spin-dependent nature of the formation of ${X}^{\ensuremath{-}}.$ If the electron density is relatively low and the emission intensity of ${X}^{\ensuremath{-}}$ is comparable to that of X, the circular polarization degree of X and ${X}^{\ensuremath{-}}$ emissions is considerably smaller. This fact is interpreted as due to a depolarization of the excess electron spins, which is induced by the spin relaxation of ${X}^{\ensuremath{-}}.$