Investigation of II –VI alloy lattice dynamics by IR spectroscopic ellipsometry

Optical properties related to lattice vibrations of bulk Zn_1‐xBe_xSe, Zn_1‐x‐yBe_xMn_ySe and Cd_1‐xBe_xSe alloys are reported. Optical phonons of the mixed crystals grown by the Bridgman method have been investigated by infrared spectroscopic ellipsometry in the wave‐number range 300‐8000 cm^‐1. The complex dielectric functions can be reproduced using a model with two or three classical damped oscillators corresponding to the BeSe‐like transverse‐optical phonon‐modes and a Drude contribution from the free carriers. The frequencies of longitudinal‐optical phonons have been found from the imaginary parts of the dielectric loss functions. The influence of the alloy composition on the zone‐centre optical phonon frequencies is discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)