We report applications of the micro-Raman technique to study the compositio
nal dependence of phonon modes in graded AlxGa1-xP layers. The dependence o
f the phonon frequencies on the Al content was monitored in a single sample
for two different crystallographic orientations. The measured compositiona
l dependence of the LO and TO phonon frequencies are in good agreement with
results of calculations based on the Modified Random Element Isodisplaceme
nt (MREI) model. The Raman spectra of the samples reveal also the existence
of other features due to disorder.