We investigated the influence of stress an the,acoustic wave propagation in
single crystalline heterostructures using a transfer matrix method. Both R
ayleigh-type and Sezawa modes exhibit an acoustoelastic anomaly, where the
stress-induced change of the phase velocity is maximum for finite film thic
knesses, considerably smaller than the acoustic wavelength. For Ge/Si(001)
compressed by I GPa the velocity shift of Sezawa modes reaches exceptionall
y high values of about 2%. These results demonstrate the importance of stre
ss effects on the determination of elastic constants of thin film heterostr
uctures.