Determination of BeTe phonon dispersion by Raman spectroscopy on BeTe/ZnSe-superlattices

We present an investigation of the vibrational properties and the elastic constant c11 of BeTe. For this purpose we applied Raman spectroscopy on folded acoustic phonons (FAPs) and confined optical phonon modes in BeTe/ZnSe superlattices. This method yields basic BeTe vibrational properties as well as the interface properties at the BeTe/ZnSe junctions. The exact values of the superlattice periodicity were obtained from X-ray diffraction, while transmission electron microscopy data supplied the individual thicknesses of the ZnSe and BeTe layers. The acoustic phonon dispersion in BeTe was determined from the FAP frequencies in the Raman spectra, together with the periodicity and the thickness ratio of the SL as well as the well known elastic constants of the ZnSe layers. We obtained for the BeTe sound velocity the value of 4180 ± 200m/s. This value was used to calculate the BeTe elastic constant c11, yielding 8.9 ± 0.9 × 1010N/m2.