Optical studies of carrier and phonon dynamics in Ga1-xMnxAs

We present a time-resolved optical study of the dynamics of carriers and phonons in Ga1−xMnxAs layers for a series of Mn and hole concentrations. While band filling is the dominant effect in transient optical absorption in low-temperature-grown GaAs, induced absorption by trapped electrons become important with increasing Mn concentration in Ga1−xMnxAs, as inferred from the sign of the absorption change. We find that carrier trapping and trapped carrier recombination becomes faster as Mn concentration increases in GaMnAs. We also report direct observation on lattice vibrations in Ga1−xMnxAs layers via the reflective electro-optic sampling technique. The data show increasingly fast dephasing of longitudinal-optical phonon oscillations for samples with increasing Mn and hole concentration, which can be understood in term of phonon scattering by the holes.