Spin relaxation in charge-tunable InP quantum dots

Abstract

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.

Electron and hole spins in InP/(Ga,In)P self-assembled quantum dots

“…This value is slightly less than the reported exciton radiative lifetime of 350-450 ps measured on a single InP/Ga 0.51 In 0.49 P QD, 15 and agrees well with the 280-330 ps exciton recombination lifetime deduced from TRPL experiments performed on an ensemble of InP/Ga 0.5 In 0.5 P QDs. 16,17 This also shows that electronic coupling between the QDs in the five-layer stack, which may be expected for only 5-nm-thick Ga 0.51 In 0.49 P spacers between the dot layers, is not relevant. Most likely such coupling effects are negligible because of off-resonance between the confined carrier levels in the different layers at least for the vast majority of dots in the ensemble.…”

Dominant role of the shear strain induced admixture in spin-flip processes in self-assembled quantum dots

“…Spin relaxation and dephasing in self-assembled QDs is of particular interest, since these decoherence phenomena set the ultimate limit on the functionality of any nanoscopic spinbased devices. Experiments show exciton spin life times much longer than the recombination times 21 and electron spin relaxation times in the range from nanoseconds 22 to microseconds 23 or even milliseconds 3,24 , depending on the material systems and experimental details. The measured spin coherence times are much shorter, on the order of nanoseconds, which is due to hyperfine-induced dephasing and ensemble inhomogeneity 8,25,26 .…”

Hanle effect in (In,Ga)As quantum dots: Role of nuclear spin fluctuations

“…For optical pumping in a magnetic field perpendicular to the optical axis, the electron spin polarization is usually destroyed with increasing magnetic field (Hanle effect). In this case the Overhauser field modifies the width and shape of the dependence of the circular polarization of the PL on the magnetic field (Hanle curve), which can become non-monotonous and even hysteretic 1,[5][6][7][8][9][10][11][12][13] The Hanle effect in presence of nuclear spin polarization in bulk semiconductors and quantum wells has been theoretically treated in the model of mean Overhauser field, which has provided good qualitative and quantitative agreement with experimental data. The validity of the mean-field approach in these systems is justified by the fact that the correlation time τ c of the electron spin at the position of a certain nucleus is much shorter than the electron's spin lifetime T s .…”