Anomalous mode in the Raman and ir spectra of mercury telluride

We discuss the origin of the low-frequency mode occurring at ~108 cm-1 (at 77 K) in HgTe and Hg-rich Hg1-xCdxTe. Through temperature- and wavelength-dependent Raman spectra and their analysis, we show that this feature is a combination phonon and acquires significant Raman (ir) activity as a consequence of a Fermi resonance with the TO phonon. Within this framework we are able to explain its TO-phonon-like behavior, and the variation of its frequency, width, and intensity with temperature