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Lattice Dynamics and Bond Polarity of Be‐Chalcogenides A New Class of II–VI Materials
Author(s) -
Wagner V.,
Liang J. J.,
Kruse R.,
Gundel S.,
Keim M.,
Waag A.,
Geurts J.
Publication year - 1999
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/(sici)1521-3951(199909)215:1<87::aid-pssb87>3.0.co;2-d
Subject(s) - phonon , raman spectroscopy , chemistry , condensed matter physics , dielectric , polar , lattice (music) , polarity (international relations) , materials science , physics , optics , optoelectronics , quantum mechanics , acoustics , biochemistry , cell
Be‐chalcogenides take a special place among II–VI compounds due to their expected reduced polarity. We report on an investigation of the phonon properties and dielectric constants of BeSe and BeTe by far‐ and mid‐infrared reflectance and Raman spectroscopy. For comparison with our experimental results we performed first‐principles calculations (LDA) to obtain the charge distribution and the TO‐phonon frequencies within the frozen phonon approximation. From the spectroscopic data we derive bond polarities, which are distinctly reduced with respect to classical II–VI compounds (ZnTe, ZnSe). They approach values of III–V compounds, such as GaAs. These results are also reflected in the calculated charge distributions. The least polar compound BeTe exhibits a very high frequency and narrow optical phonon band due to the extraordinary mass ratio m Be = 9.0 amu versus m Te = 127.6 amu. Therefore, in BeTe, in contrast to almost all other II–VI compounds, the standard optical phonon decay channel into two acoustic phonons with opposite momenta is not possible. We investigated the consequences for the temperature behaviour of the optical phonon parameters.