Phonon Dispersion Curves of BeSe and BeTe

Abstract

Subject classification: 62.20.Dc; 63.20.Dj; 71.20.Nr; S8.12; S8.13 The purpose of our study is to calculate the phonon dispersion curves of BeSe and BeTe. Owing to the few available data, a simple model demanding only a reduced set of force constant-parameters is required. A well-adapted model is the one of De Launay (Solid State Phys. 3, 203 (1957)) based on atomic central and angular forces. The model has been implemented by introducing the polarization field into the dynamical equations for the longitudinal modes.Introduction Wide-band-gap semiconductors are currently under intense investigation for optoelectronic applications in the blue-UV range. Among II-VI compounds, ZnSe and related materials have attracted the most attention. Recently, beryllium chalcogenides (BeSe, BeTe) came under focus because they exhibit covalent bonding, which is quite unique among II-VI compounds. Their development, however, relies on a detailed knowledge of the physical properties of the materials which is still lacking. In fact BeTe and BeSe compounds remain basically unexplored, probably because of the difficulty in obtaining them as single crystals or epitaxial layers. The method chosen for calculating the phonon dispersion curves has already been successfully used in the dynamical study of graphite intercalation compounds [2] but before applying it to the chalcogenides, care was first exercised to provide definitive confidence in the model. Its pertinent character was checked by taking input data for ZnSe the same as those now available for BeSe. This corresponds to a reduced set of phonon frequencies, related to the zone-centre optical modes and the zone-edge acoustic modes, in addition to the C 11 elastic coefficient.

Study on structural, mechanical, electronic, vibrational, optical and thermo-dynamical behaviour of ZB Structured BeZ (Z=S, Se and Te) using ATK-DFT

“…From Figure 4 and Table 4, it is evident that both the calculators LDA and GGA have similar values of phonon frequencies for BeS and closer values for BeSe and BeTe. Our results are in good agreement with experimental results [49][50] and preferably excellent as compared to other theoretical results [5,7,10,[50][51][52] for the major symmetry points. From Figure 4 and Table 4, it is predictable that the dispersion of transverse (TO) and longitudinal optical phonon (LO) increases upward in the sequence of BeS→BeSe→BeTe along Γ-X with respect to acoustic and optical phonons and the similar characteristics were confirmed by Srivastava et al [7].…”

Optical and vibrational properties of Be-Zn chalcogenide alloys and superlattices

“…In Be chalcogenides, although significant amount of Raman 7,49-57 and IR data 32,33 on the vibrational properties exist in the literature and a few theoretical studies attempted, [45][46][47] the complete description of lattice dynamics is, however, still rather scarce. Again, despite the existence of limited experimental data on ͑BeTe͒ m / ͑ZnSe͒ n , the dynamical behavior of isoanion ͑BeSe͒ m / ͑ZnSe͒ n SLs has not been adequately investigated either experimentally or theoretically.…”

“…35,36 First-principles pseudopotential calculations [37][38][39][40][41][42][43][44] have been used to investigate structural, elastic, and electronic properties of the zincblende phase of Be chalcogenide materials. Unfortunately, very limited information exists on the vibrational and thermodynamic properties [45][46][47] of Be-Zn chalcogenides. For instance, the Debye temperature D is a fundamental physical property used to distinguish between the high-and lowtemperature regions of any material.…”

“…In the absence of experimental results on the thermodynamic properties a few theo-retical attempts have been made recently. The lattice dynamics study of BeSe and BeTe reported earlier by Doyen-Lang et al 45 have used a simplified phenomenological De Launay 48 model with two ͑central and angular͒ force constants. Wagner et al 46,47 calculated the zone-center TO phonon values for BeSe and BeTe by using first-principles calculations, based on frozen-phonon approximation within the pseudopotential scheme and the density-functional theory ͑DFT͒.…”

“…7,[42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] Of particular interest are the TO modes as they consist of quasi-independent oscillators exhibiting 1-bond→ 2-mode behavior in the percolation scheme. 7,[42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] In Be x Zn 1−x Se͑Te͒ alloys this atypical phonon mode behavior is explained recently by Pagès et al 49 by using a double-branch percolation model which discriminates between vibrations within the randomly formed hard Be-rich host region and the soft Zn-rich region. Here we have used a traditional formulation of the multilayer 66 optics with appropriate alloy dielectric functions and calculated the IR reflectance spectra of thin Be x Zn 1−x Se/ GaAs͑001͒ epilayer at an oblique incidence ͑cf.…”