The spin dephasing relaxation in single-electron-doped InP quantum dots was studied by means of Hanle measurements. When an InP quantum dot is doped with one electron on average, a narrow Lorentzian dip with half-width of 4.6 mT appeared and was superposed on two Lorentzians with half-widths of 1.54 and 128 mT in the Hanle curve. The half-widths 1.54 T, 128 mT, and 4.6 mT are ascribed to spin-dephasing relaxation of holes, electron-hole pairs, and doped electrons consistuting negative trions, respectively. The corresponding spin coherence time of the doped electrons at 5 K is 1.7 ns, which is determined by the frozen fluctuation of nuclear spins in the quantum dots. With increase of temperature, the spin-dephasing rate of the doped electrons increases.

Spin relaxation of electrons doped in InP quantum dots was studied by means of luminescence pump-probe and Hanle measurements. Optical pumping makes spins of doped electrons to be oriented in parallel to the helicity of the circularly polarized excitation. The luminescence pump-probe showed the spin orientation of the doped electrons decay on a millisecond time-scale. Hanle measurement clarified the spin dephasing relaxation time of doped electrons is 1.7 ns which is explained by the frozen fluctuation of nuclear spins.Comment: 3 pages, 2 figures, presented in ICPS-200

Spin relaxation in charge-tunable InP quantum dots was studied for quasiresonant excitation by means of both static and dynamic optical orientations. In neutral and one-electron-doped dots, spin relaxation of photogenerated electron-hole pairs takes place with a decay time of ϳ45 ps through phonon-mediated energy relaxation. In neutral dots, spin flip of single-particle holes additionally takes place and dark excitons are formed. Dark excitons work as spin reservoir and produce negative circular polarization under a small transverse magnetic field ͑B͒. Spin orientation produced by optical pumping of the resident electrons in oneelectron-doped dots manifests negative circular polarization near B = 0 and long coherence time of 1.7 ns for doped electron spins is observed. In two-electron-doped dots, spin dynamics is dominated by hole-spin relaxation in the lowest quantum state with a decay time of ϳ50 ps.