Using micro-Raman scattering, we have investigated the vibrational properties of nominal In, 1-x-yGaxAlyAs (x = 0.13, y = 0.34) layers that were grown lattice matched to InP (100) substrates by molecular-beam epitaxy. In order to control and optimize crystalline quality of these layers, the quaternary alloy films were also grown on (100) substrates oriented 1degrees, 2degrees, 3degrees, and 5degrees toward the [(1) over bar1] direction. Atomic force microscopy has been employed to investigate the surface topography. The micro-Raman technique has been applied to evaluate the quality of these epitaxial films. Optical phonons show three-mode behavior in these quaternary alloys and the dominant bands observed in the spectra are of three binaries, namely, the GaAs-, InAs-, and AlAs-like optical phonons. The narrowest Raman linewidth and much weaker forbidden modes observed in the layer grown on InP(100) oriented 2degrees toward the [(1) over bar 10] direction, suggest the best crystalline quality among the quaternary alloys grown on misoriented substrates. (C) 2004 American Vacuum Society.