Spin dynamics of carriers in GaAs quantum wells in an external electric field

Abstract

The effect of external electric bias on the kinetics of circularly polarized photoluminescence (PL) of the GaAs quantum wells (QWs) is studied experimentally. It is found that a negative bias applied to the top surface of the samples causes the appearance of a slow component in the decay of the PL circular polarization. The amplitude of this component grows with the bias ${U}_{\mathrm{bias}}$ and reaches nearly 100% at ${U}_{\mathrm{bias}}=\ensuremath{-}2\mathrm{V}.$ In a transverse magnetic field, the polarization decay shows oscillations related to the spin precession. The changes in the shape of the oscillations with the applied bias indicate a transition from the exciton spin precession to that of the electron spin. Based on the analysis of the experimental data, we came to the conclusion that the external electric field reduces the exchange coupling between the electron and hole spins. As a result, the hole spin exhibits fast relaxation whereas the electron spin holds its light-induced orientation for a relatively long time. The studies of the electron spin dynamics in oblique magnetic fields have allowed us to estimate the effective energy of the electron--hole exchange interaction in the electric field created by the bias ${U}_{\mathrm{bias}}=\ensuremath{-}2\mathrm{V}.$ The exchange splitting thus obtained is much smaller than typical exchange splittings of the excitonic states in the GaAs QWs.