Ultrafast carriers dynamics in GaSb/Mn random alloys

Single color time resolved reflectivity change (ΔR/R) measurements were performed at room temperature for two wavelength regions, 1.35-1.60 μm and 750 - 860 nm. The long wavelength measurements show that consistent with other low temperature (LT) grown III-V's, the GaMnSb samples have somewhat shorter recombination times (τ_r < 2 ps) than the high temperature grown GaSb buffer layer (τ_r ∼ 28 ps at 1.6 μm). The recombination time decreases with increasing doping concentration. ΔR/R time dependence near the band edge indicates a possible metastable defect state produced after photo-excitation. For the measurements in the 750-860 nm range, ΔR/R has periodic oscillations for both in GaMnSb and epilayer samples. The oscillation period (T) is independent of the Mn concentrations, but dependent on the probe photon energy with T = 21 ps, 24 ps, and 25 ps for GaMnSb samples, and T = 19.3 ps, 20.5 ps, 22.0 ps for the epilayer sample at the probe wavelengths of 750 nm, 800 nm, and 860 nm, respectively. These values are in good agreement with recent theoretical calculations for modulation of ΔR/R due to coherent generation of acoustic phonon wave packets.