Long wavelength longitudinal optical (LO) and transverse optical (TO) phono
ns of BeSe and ZnxBe1-xSe layers are identified in a wide composition range
by using Raman spectroscopy. A two-mode behavior is clearly evidenced. As
predicted by the dielectric model of Hon and Faust, the eigenfrequencies of
the BeSe- and ZnSe-like LO modes correspond to the maxima of Im <-epsilon(
omega, x)(-1)>. Excellent agreement is obtained with a model where the calc
ulations are performed by using the equations of motion and polarization de
rived from the modified random element isodisplacement model. Besides, the
TO and LO frequencies for BeSe are determined to be 501 and 579 cm(-1), res
pectively. (C) 2000 American Institute of Physics. [S0003-6951(00)04030-4].