Vibrational properties of HgCdTe system

Abstract

The results of reflection spectra at 300 °K in the far-infrared region (100–400 cm−1) are reported due to low concentration of Hg atoms in the Cd-rich CdHgTe mixed crystals. A gap mode is observed at 131 cm−1 due to isolated Hg occupying Cd in CdTe. The experimental results are analyzed theoretically using the well-know Green’s function technique. The perturbation caused by low concentration of Cd(Hg) is described by the mass change at the impurity site as well as local variation of impurity-host interactions. In the nearest neighbor approximation, all the involved Green’s function matrix elements have been computed numerically by incorporating the lattice phonons from an eleven parameter rigid-ion model fitted to recent neutron data of HgTe and CdTe. We find that different substitutional defects in Hg-Cd tellurides can give rise to well-defined symmetry vibrations both within the gap and outside the maximum phonon frequency regions. Our calculations suggest that a gap mode of Hg substituted to Te is likely to be the possible explanation for the origin of the observed Ω2 mode in HgTe. In the cases of known experimental data (viz., CdTe:Hg and HgTe:Cd) we have estimated the nature of force perturbations and the results are compared and discussed with those obtained from a modified-random-element isodisplacement model.