The band structure of a layered Hg₃TeCl₄ crystal formed by energy states of HgCl₂ and HgTe crystals

Abstract

The ab‐initio calculated band structure of a not as yet investigated orthorhombic Hg3TeCl4 crystal (Pbca, D152h) was analyzed by means of the elementary energy‐bands concept. It was demonstrated that this band structure originates from that of a layered HgCl2 dielectric deformed by the presence of the HgTe structural elements. Further, it was revealed that the valence band of Hg3TeCl4 is composed of the 8‐branch elementary energy bands corresponding to the actual Wyckoff position c (x, y, z) of D152h group that indicates the presence of ionic and covalent contributions to the chemical bonding in the crystal. The existence of Davydov splitting in the 8‐branch elementary energy band situated in the low‐energy range of the valence band was observed, which is typical for layered crystals with a weak interlayer interaction between translationally nonequivalent structural units. It was shown that the anisotropy of the electron and hole effective masses does not correspond to the macroscopic anisotropy of the crystal and an explanation of this behaviour was proposed. The obtained parameters of the crystal (direct energy gap Eg = 2.49 eV as well as values of the estimated electron effective masses) indicate that it could find an application in optoelectronics. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Band Structure and Optical Properties οf the Layered Hg3TeCl4Crystal

“…Mechanical properties of the crystal as well as the X-ray investigations point to its layered properties, there are 64 atoms in the unit cell which are arranged into two double, translationally non-equivalent layers perpendicular to the y axis. It was shown that the anisotropy of the overlap of electron wave functions is different in various energy ranges and leads to the Davydov splittings in the band structure, in particular in the Γ point of the conduction band [2,3]. Hence, the anisotropy of the electron and hole effective masses does not correspond to the mechanical anisotropy of the crystal and it is not typical for layered crystals (m 2 (hν) dependence points to the presence of the direct optical transitions in the crystal which is in agreement with the theoretical band structure calculations.…”

“…Properties of this crystal have been not investigated experimentally so far, except its crystalline structure [1]. From the ab initio band structure calculations within a framework of density functional theory (DFT) follows that Hg 3 TeCl 4 is a wide band-gap layered photoelectric with a smallest band gap located in the Γ point of the Brillouin zone [2]. Hence, a characteristic dependence of the absorption coefficient α on hν as well as the inter-band photoluminescence should be expected for this crystal.…”

Relation between the topology of the elementary energy bands in the valence band of the Hg3TeCl4 crystal and its anisotropy

“…This sequence will be further used to explain the topology of the 8-branch EEBs and their separation into two 4-branch EEBs in a given energy range. The obtained picture of the Davydov splitting in the EEBs in the BZ will be verified with the numerical band-structure calculation results of the D (Pbca) space group describing the symmetry of the crystal, and the presence of two double, translationally nonequivalent atomic layers in the unit cell, perpendicular to the y-axis [1]. The space group describing the symmetry of the double atomic layer is…”

“…It has been shown that the anisotropy of the valence-band top and the conduction-band bottom as well as of the effective masses of charge carriers do not correspond to the mechanical anisotropy of this crystal [1]. Further, it was shown that the valence band is composed of some of the smallest building parts, the so-called elementary energy bands (EEBs) [2][3][4] which, in the case of 3 4 Hg TeCl , consist of 8 branches.…”

“…Recently, the ab-initio band structure of a layered, prospective for optoelectronics, 3 4 Hg TeCl crystal has been calculated in the framework of the density functional theory in the LDA [1]. Unlike other layered crystals, 3 4 Hg TeCl (Pbca,…”