Strain relaxation has been investigated by means of Raman scattering in strained InxGa1-xAs layers (with x ranging from 0 to 1) grown on In0.53Ga0.47As/InP (001). The epilayers are either under tensile (x < 0.53) or compressive (x > 0.53) strain. Relaxation coefficients have been deduced from the frequency shifts of the GaAs-like optical phonons. A marked dissymmetry in strain relief is found over the whole composition range between equivalent tensile and compressive misfits. Disorder activated Raman scattering features have been analyzed and correlated to the structural defects resulting from the strain relief in the two and three-dimensional growth modes. Strain : inhomogeneities resulting from surface corrugation are evidenced by micro-Raman measurements on layers with tensile misfits. (C) 1997 American Institute of Physics.