Two-phonon processes in II-VI semiconductors investigated with terahertz time-domain spectroscopy

The authors investigate via terahertz time-domain spectroscopy the temperature dependent FIR properties of the II-VI semiconductor compounds ZnTe and CdTe in the frequency range 200 GHz -2.3 THz. At frequencies below the first transverse optical phonon resonance, the absorption and dispersion show resonance features in addition to the fundamental phonon mode. Gallot et al. (1999) assigned the 1.6-THz absorption band in ZnTe to a fundamental phonon mode. In this paper, the authors categorize this absorption band and other spectral features below the transverse optical resonance as second-order phonon interactions between acoustical and optical modes. The authors use the different temperature behavior of the two-phonon processes to distinguish between sum- and difference modes. This is experimentally realized by using a standard THz spectrometer.