Intrinsic point defects often play a significant role in determining  the properties of mercury-containing  solid solutions such as HgCdTe or HgZnTe,  which are fundamental materials for infrared (IR) devices. An IR spectrum may provide useful information concerning the presence of defects and their influence on phonon spectra, as already demonstrated in CdHgTe and ZnHgTe¹ alloys as well as in hydrogenated CdTe-monocrystals². In this paper we report and discuss far-infrared (FIR) experimental spectra of both HgCdTe and HgZnTe ternary alloys where additional modes induced by Hg-vacancies have been clearly detected.

FIR reflectivity experiments were performed at the DAFNE-light laboratory at Frascati (Italy). We used a BRUKER Equinox 55 FT-IR interferometer modified to collect spectra in vacuum. We used as IR sources both the synchrotron radiation from the DAFNE storage ring, and a mercury lamp. Measurements were performed over a  temperature range of 20-300 K and for frequencies ranging from  50 to 600 cm^-1.

We present a non-destructive method for  quantitative determining the vacancy concentration in the lattice of Hg-based semiconductor alloys with  tetrahedral structure. The method is based on the identification of additional vibrational modes (AVM) induced by lattice deformations in the far infrared (FIR) reflectivity spectrum. Although the method is restricted by sensitivity limitations, recent FIR experimental data carried out on HgZnTe and HgCdTe samples containing Hg-vacancies confirmed the presence of AVMs induced by Hg-vacancies in  as-grown crystals.

[1] J. Cebulski, E. M. Sheregii, J. Polit, A. Marcelli, M. Piccinini, A. Kisiel, I. Kucherenko,

     R. Triboulet, APPL. PHYS. LETT.  92, 121904  (2008).

[2] J. Polit, E.M. Sheregii, J. Cebulski, B. Robouch, A. Marcelli, M. Cestelli Guidi,

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1. Discontinuity of the phonon mode frequency temperature dependence caused by a zero-gap state in HgCdTe alloys
2. Influence of hydrogen on hydrogenated cadmium telluride optical spectra
3.  Far-infrared reflectivity as a probe of point defects in Zn- and Cd-doped HgTe
4. SR a brilliant sources for solid-state researches in the IR and far-IR energy domain 
5. Additional  Phonon Modes related to intrinsic defects in CdHgTe
6. Phonon and vibrational spectra of real crystals obtained using the synchrotron radiation
7. Structural and Electric Fieeld-Induced Properties of the narrow-Gap Semiconductor ZnCdHgTe Thin Films
8. Influence of hydrogen on optical spectra of hydrogenated CdTe
9. The local crystalline structure of ZnCdTe alloys obtained by Far Infrared Synchrotron Radiation measurements
10. Defects induced by oxygen and hydrogen in CdTe crystals