Spatially resolved Raman spectroscopy at room temperature is used to study quantum well intermixing in GaAs:AlAs superlattice structures. Phonon modes are probed from the side facet along the  direction. The intermixing leads to the appearance of interfacial alloy modes and degraded the intensity of the superlattice interface (IF) modes, which can be used as a sensitive indicator of superlattice quality. These changes in the Raman spectra, along with spatially resolved photoluminescence, are used to distinguish the degree of intermixing in samples intermixed by impurity free vacancy diffusion at 850–950 °C, and to investigate the bandgap modulation in a periodically intermixed bandgap grating fabricated using ion implantation induced disordering. The shift of the GaAs-transverse optic mode to the GaAs-like transverse optic alloy mode and the degradation of the GaAs-IF mode are shown to provide the best indication of the extent of intermixing. Due to the large contrast in the GaAs-IF mode intensity between as-grown and intermixed superlattice, using IF modes is found to be a promising route for characterizing the resolution of the superlattice bandgap grating.