Spatial and temporal diffusive spin dynamics in the transient regime for 10-nm-wide InGaAs/InAlAs quantum wells were investigated using time-resolved optical Kerr rotation (TRKR) microscopy. The transient regime of diffusive spin dynamics is a specific regime which appears after local excitation but before the formation of a spin mode. In this regime, the spin precession frequency induced by the spin–orbit (SO) magnetic field decreases with time since the diffusive velocity decreases as the distribution of spins expands. In this study, by decreasing the spot size of the excitation pulse, we examined the spin dynamics in the transient regime. We carefully analyzed the TRKR signals using time-dependent frequency equations established by Kohda et al. [Appl. Phys. Lett. 107, 172402 (2015)]. All the TRKR signals could be well reproduced by the time-dependent frequency equations. Our analysis reveals that the spin precession frequencies arising from the SO interaction gradually decrease with time, and they allowed the extraction of the Rashba and Dresselhaus SO parameters. We revealed that SO parameters can be extracted accurately via scanning measurements in the diffusive motion of local spin excitation even in the time periods before the appearance of the spin mode.

The deriving method of spin–orbit (SO) parameters using a single-frequency analysis was examined in a transient regime of diffusive spin dynamics in InGaAs/InAlAs multiple quantum wells. Transient regime of diffusive spin dynamics is the time regime when the spin precession frequency induced by SO magnetic fields decreases and changes with time. Recently, we have established a method of deriving SO parameters by scanning time-resolved Kerr rotation microscopy in this transient regime [Kawaguchi et al., Appl. Phys. Lett. 115, 172406 (2019)] using the time-dependent spin precession frequency analysis. Although reliable SO parameters were derived, time-independent single-frequency analysis is still attractive because of its simplicity. In this paper, SO parameters’ derivation was performed by the single-frequency analysis comparing the experiment and the Monte Carlo (MC) simulation. The best fit of the simulation to the measurement for the SO-induced frequency yields the derivation of SO parameters; however, the derived values were different from the reliable SO parameters derived by the time-dependent analysis. This discrepancy arises from a spin relaxation time difference between the experiment and MC simulation. After intentionally adjusting the spin relaxation time of the MC simulation to the experiment, the SO-induced frequency obtained by the MC simulation with reliable SO parameters reproduced the experiment well. We found that the spin relaxation time adjustment of the MC simulation to the experiment is necessary to obtain accurate SO parameters from the single-frequency analysis comparing the experiment with the MC simulation.

Temperature and laser energy dependencies of electron g-factors are investigated for the conduction band of In0.53Ga0.47As/In0.52Al0.48As quantum wells using the time-resolved Faraday rotation (TRFR) technique. We found that in- and out-plane g-factors are ∼−3.20 and ∼−3.50 at a temperature of 5 K for the 12-nm wide quantum wells in a tilted sample configuration of the TRFR measurement. A comparison between the experiment and the eight-band Kane model calculation shows that the thermal distribution and dilatational change of the energy gap play an important role in explaining the temperature dependence of optically measured g-factors. We also found that the measured g-factor is influenced by the laser wavelength, which clearly shows that detection energy is the one of the significant factors for determining the optically measured g-factor.

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