Electronic band structures and electron spins of InAs/GaAs quantum dots induced by wetting-layer fluctuation

摘要

Electronic band structures and spin states of the InAs/GaAs quantum dots (QDs) induced by the wetting-layer fluctuation were investigated by employing the technique of time-resolved Kerr rotation (TRKR) with and without magnetic field. Sign change of the Kerr rotation signal was unambiguously observed when only the wavelength of the pump/probe light was scanned. By carefully examining the dependence of TRKR signal on the excitation wavelength and magnetic field as well as photoluminescence and reflectance spectra, the physical origin causing the sign change of the Kerr signal is uncovered. It is due to the resonant excitations of electrons with opposite spin orientations at heavy- (hh) and light-hole (lh) subbands, respectively, since there is a large enough energy separation in QDs for the excitation laser pulses. This measurement also leads to a precise determination of the energy separation between the hh and lh subbands near k = 0 point in the dots.