Near-field spectroscopy of single self-assembled InAs quantum dots: Observation of energy relaxation process

We have investigated carrier relaxations in single InAs/GaAs self-assembled quantum dots using near-field optical spectroscopy. Polarized PL spectroscopy of Zeeman splitting peaks with an external magnetic field allows us to investigate spin relaxation in the excited states. The excitation energy dependence of the polarization of each spin component shows suppression of spin flipping during the relaxation of carriers inside the quantum dots. The result also suggests different spin relaxation processes between in the quantum dots and in a wetting layer.