Room-temperature ultrafast carrier and spin dynamics in GaAs probed by the photoinduced magneto-optical Kerr effect

The picosecond and subpicosecond dynamics of spins in intrinsic and n-doped GaAs is investigated at room temperature using the time-resolved, pump and probe, photoinduced, near-resonant magneto-optical Kerr effect between 1.44 and 1.63 eV. Three components with different temporal and spectral behavior are distinguished in both Kerr rotation and ellipticity, and their origin is discussed in relation with theoretical predictions and simulations. Two contributions are attributed to the splitting of the spin sublevels. The first one, present only as long as pump and probe pulses coincide in time, is a coherent response accounted for in terms of the optical Stark effect, whereas the longer decay of the second one, up to 35 ps, is attributed to electron spin relaxation. The third component is assumed to arise from the difference in population of the photoexcited states and decays within a time smaller than the pulse duration, which is attributed to the energy relaxation of electrons towards the bottom of the conduction band through carrier-carrier and carrier-phonon scattering.