All-optical control of the exciton g-factor in InAs/GaAs quantum dots

In this work, we show that an electric field can be used to tune the g-factor in (In,Ga)As quantum dots and that one can even change its sign. We measure the degree of circular polarization of photoluminescence of quantum dots in a magnetic field. The quantum dots are grown in the center of a GaAs p–i–n structure and they experience, therefore, a built-in electric field. This electric field can be compensated by photo-created charge carriers. The circular polarization changes as the excitation density is increased, and eventually changes its sign, which is interpreted as a change of sign of the exciton g-factor. This sign change is associated with the electric field, since the Stark shift in the photoluminescence spectrum occurs in the same excitation density range as the polarization sign change. Furthermore, we extract a longitudinal spin relaxation time T1T1 of 10.1 ns. A time-resolved Kerr rotation spectroscopy measurement yields an in-plane g-factor for the electron in the range 0.3–0.4 and a decoherence time T2T2 in the range 500–800 ps.