Impact of Magnetic Impurities on Transient Propagation of Coherent Acoustic Phonons in II-VI Ternary Semiconductors

We detail our studies on the transient propagation of coherent acoustic phonons (CAPs) in Mn-doped Cd1–xMnxTe [(Cd,Mn)Te] diluted-magnetic and pure CdTe semiconductors. The CAPs were generated by femtosecond optical pulses and then time-resolved using oneand two-color pump-probe spectroscopy. Intrinsic lifetimes on the order of at least tens of nanoseconds of CAP oscillations were observed in (Cd,Mn)Te by pumping above and probing below the crystal bandgap. The CAP oscillation characteristics were well described by the propagating-strain model with the electronic stress as the excitation mechanism. Fitting the CAP frequency dependence on the probe wave vector while including the dispersion effect of the (Cd,Mn)Te refractive index, resulted in a very accurate determination of the crystal acoustic-phonon velocity and its increase with the Mn-doping increase, as well as the temperaturerelated changes of the acoustic velocity in pure CdTe single crystals.