Spin orientation in charge-tunable InP quantum dots

Spin polarization in charge-tunable InP quantum dots (QDs) was investigated as a function of the longitudinal magnetic field under the linearly polarized excitation. In neutral QDs, photoluminescence (PL) polarizes resonantly at two magnetic fields where bright and dark excitons anticross each other. The resonant spin-orientation structure turns from up to down with the change of the observation photon energy, reflecting the size-variable g-factor of holes in InP/InGaP QDs. In one-electron doped QDs, on the other hand, PL polarization linearly increases with the increase of magnetic field. In two-electron doped QDs, small differential structure coming from the electron–hole anisotropic exchange interaction is superposed on the linear increase of PL polarization versus magnetic field. The linear slope observed for trions and tetraons is smaller than that expected for holes uncorrelated with the electron spins and thermalized in Zeeman sublevels and is reduced by the electron–hole exchange interaction at low temperatures.