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Spin coherence of resident electrons and holes is measured in ZnSe-based quantum wells by means of time-resolved Kerr rotation technique. At a temperature of 1.8 K spin dephasing time for localized electrons can be as long as 33 ns, and for holes of 0.8 ns. Electron spin precession is clearly observed in a wide temperature range up to 230 K. The electron spin dephasing becomes much shorter of 0.2 ns for the quantum well with a high-density electron gas. Using vector magnet all components of the g-factors tensor are evaluated for the electrons and heavy-holes, revealing strong anisotropy for the heavy-holes.

Spin coherence has been studied in self-assembled (In,Ga)As/GaAs quantum dots which contain on average a single electron per dot due to n-type modulation doping. A magnetic field was applied in the Voigt geometry, in order to study the precession of the electron spins which are oriented normal to the field. Here we address the mechanism by which such a normal orientation can be achieved by resonant excitation with circularly polarized laser pulses. Further, we discuss, how long this coherence is maintained within an ensemble of quantum dots. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Electron spin coherence has been studied in CdTe/(Cd,Mg)Te quantum wells with a low-dense two-dimensional electron gas by means of pump-probe Kerr rotation technique. Spin dephasing time of 30 ns has been measured in the limit of zero magnetic fields and at a temperature of 1.9 K.

We report on spin memory relaxation time τ s of free electrons in CdTe-based quantum wells which is found to be in the nanosecond range. In these studies two different techniques have been exploited: (i) the Hanle effect under cw excitation and (ii) the time-resolved pump-&-probe Kerr rotation measured under excitation by 1.8-ps optical pulses. These independent techniques give very close results τ s =19 ns and τ s = 14 ns, respectively. To our knowledge this is by two orders of magnitude longer than the electron spin relaxation times reported for CdTe-based quantum wells so far.