Quasi-binary alloy HgCdTe (MCT) form a continuous series of solid solutions of
Hg_1-xCd_xTe over x = 0 to 1 with zinc-blend crystalline structure¹. In these alloys a band inversion and, as a result, a zero-gap state E_g ≡ G₆ – G₈ = 0 is realised as a composition varies from HgTe to CdTe. The zero-gap state depends on temperature too because there are several dependences E_g (x,T) for that is realised E_g = 0. These type of peculiarity can be realised by changing of E_g using press or temperature.

In this work are presented experimental results of optical reflectivity in far-infrared region (FIR) in wide interval of temperature (from 10 K to 290 K with step 10 K) for sample of Hg_1-xCd_xTe (x=0.115). For observation of effects described above a synchrotron radiation  FIR source has a great advantage as compared with the classical sources, intensity of which drops abruptly in this spectral region. Obtained results evidently show that frequencies of optical phonon modes have discontinuity in their temperature dependence when the zero-gap state takes place.

1.R. Dornhaus and G. Nimtz, Narrow Gap Semiconductors, Springer-Verlag, Berlin 1985,     v. 98, p. 159.

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