OPTICAL AND ACOUSTICAL PHONON PROPERTIES OF BETE

We present an investigation of the vibrational properties, the elastic constant cl, and the infrared dielectric constant epsilon(infinity) O f BeTe. For this purpose we applied far-infrared reflectance and Raman spectroscopy to single BeTe layers and BeTe/ZnSe superlattices. The e xperimental data are used to access the bond ionicity in the framework of an empirical tight binding approach. A low bond polarity of 0.61 i s determined for BeTe, which corresponds to a high lattice stability. Furthermore, the elastic constant c(11) is determined as to be 8.9 +/- 0.9.10(10) N/m(2) from the frequency positions of folded acoustic pho non (FAP) modes in BeTe/ZnSe superlattices. The experimental results a re correlated to data obtained by first-principles local density appro ximation (LDA) calculations. (C) 1998 Elsevier Science B.V. All rights reserved.