Spin relaxation in charge-tunable InP quantum dots

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 photo-generated electron-hole pairs takes place with a decay time of similar to 45 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 (B). Spin orientation produced by optical pumping of the resident electrons in one-electron-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 similar to 50 ps.