Optical study of THz plasmon-phonon oscillations in semiconductors

The dynamics of coherent plasmon-phonon oscillations in compound semiconductors are investigated using a pump-probe technique. It is shown that the optically excited coherent carriers drive the thermal carriers introduced by the doping in forming coherent plasma oscillations. By analyzing the coupled oscillations with different hole densities a strong influence of electron-hole scattering on the dephasing of coherent plasmons is found. For the near-band edge detection the reflectivity change by these oscillations is strongly enhanced by the Franz-Keldysh effect. Finally, the second harmonic of the coherent longitudinal optical phonon frequency is observed as a result of the dynamical Franz-Keldysh effect.