Dynamical properties of terahertz radiation from coherent longitudinal optical phonon-plasmon coupled modes in an undoped GaAs/n-type GaAs epitaxial structure

We have investigated the dynamical properties of terahertz radiation from coherent longitudinal optical phonon-plasmon coupled (LOPC) modes in an undoped GaAs/n-type GaAs epitaxial structure using time-domain terahertz spectroscopy. It was confirmed that the frequencies of the lower and upper LOPC modes are dominated by a photogenerated carrier density. The dynamical properties of the LOPC modes, the lifetimes of which are about 0.2 ps, were examined by time-partitioning Fourier transformed spectra of the time-domain terahertz signals. It was found that the lifetimes of the LOPC modes depend on their frequencies.