Understanding and controlling the spin dynamics in semiconductor heterostructures is a key requirement for
the design of future spintronics devices. In GaAs-based heterostructures, electrons and holes have very different
spin dynamics. Some control over the spin-orbit fields, which drive the electron spin dynamics, is possible by
choosing the crystallographic growth axis. Here, (110)-grown structures are interesting, as the Dresselhaus spinorbit
fields are oriented along the growth axis and therefore, the typically dominant Dyakonov-Perel mechanism
is suppressed for spins oriented along this axis, leading to long spin depasing times. By contrast, hole spin
dephasing is typically very rapid due to the strong spin-orbit interaction of the p-like valence band states. For
localized holes, however, most spin dephasing mechanisms are suppressed, and long spin dephasing times may be
observed. Here, we present a study of electron and hole spin dynamics in GaAs-AlGaAs-based quantum wells.
We apply the resonant spin amplification (RSA) technique, which allows us to extract all relevant spin dynamics
parameters, such as g factors and dephasing times with high accuracy. A comparison of the measured RSA
traces with the developed theory reveals the anisotropy of the spin dephasing in the (110)-grown two-dimensional
electron systems, as well as the complex interplay between electron and hole spin and carrier dynamics in the
two-dimensional hole systems.
Spin dynamics in zincblende two-dimensional electron systems is usually dominated by the Dyakonov-Perel
spin dephasing mechanism resulting from the underlying spin-orbit fields. An exceptional situation is realized
in symmetrically grown and doped GaAs/AlGaAs quantum wells grown along the  direction, where the
Rashba contribution is negligible and the effective Dresselhaus spin-orbit field is perpendicular to the sample
plane. In such a system the spin dephasing times for in- and out-of-plane crystallographic directions are expected
to be strongly different and the out-of-plane spin dephasing time is significantly enhanced as compared with
conventional systems. We observe the spin relaxation anisotropy by resonant spin amplification measurements
in a 30 nm wide double-sided symmetrically δ-doped single quantum well with a very high mobility of about
3•10<sup>6</sup> cm<sup>2</sup>/Vs at 1.5K. A comparison of the measured resonant spin amplification traces with the developed
theory taking into account the spin dephasing anisotropy yields the dephasing times whose anisotropy and magnitudes are in-line with the theoretical expectations.
A controllable delivery of spins in nanodevices is required for applications in spintronics technologies. A pure spin current, in which oppositely oriented spins move in opposite directions, is a phenomenon that could be used for this purpose. Various optical techniques can efficiently excite such spin currents in bulk semiconductors and nanostructures. We here propose and analyze two new optical infrared-light techniques for the injection of a pure spin current in nanostructures. The techniques are based on the intersubband light absorption (one-photon process) and stimulated Raman scattering (two-photon process). The infrared light absorption deposits approximately 100 meV for each absorption event associated
with current injection. In the spin-flip Raman process which is possible due to spin-orbit (SO) coupling, the corresponding energy transfer to the system, is on the order of 1 meV. The stimulated Raman process depends on the electron momentum, and therefore, electrons with different spins can be launched in different directions. The infrared-injected pure spin currents can be engineered by changing the Rashba spin-orbit coupling using an external bias across the quantum well. The injected spin current should be detectable by pump-probe optical spectroscopy, and thus points the way toward the design of full-optical write-and-read spintronics devices.