First- and second-order photon-phonon interactions and optical parameters of ZnTe crystal: A broadband terahertz time-domain spectroscopy study

We performed broadband terahertz (THz) time-domain spectroscopy measurements to study the photon-phonon interactions and frequency-resolved optical parameters of bulk ZnTe. Using laser-induced plasma as the source of THz radiation and a GaP bulk wafer as the sensor crystal, a broadband THz response of bulk ZnTe wafer with thickness of 0.1 millimeter within the frequency range from 0.1 to 7.5 THz was obtained. Comparing the measured photon absorption spectrum with phonon dispersion curves obtained from ab initio calculations, we identified the first- and second-order photon-phonon interactions of ZnTe crystal. The frequency-resolved optical parameters including the complex refractive index, dielectric response and conductivity of ZnTe crystal within the frequency range between 0.1 and 7.0 THz were derived from the measured THz transmitted field. By fitting the frequency dependent dielectric functions with the Lorentz oscillator model, a static permittivity of 10.5 along with a transverse optical phonon frequency of 5.9 THz and a phonon lifetime of 1.25 picosecond were obtained for ZnTe crystal.