III-V compounds nanowires (NWs) are of central interest due to their innovative physical properties and potential applications in electronic and photo-electronic devices. Freestanding AlGaAs NWs were grown by MOVPE by the Vapor Liquid Solid method along the (111) direction on GaAs(111) substrates. Raman measurements were performed on single as-grown NWs with a scanning confocal micro-Raman spectrometer. Rayleigh imaging, was applied to locate individual NWs and define their position for Raman measurements. The spectra of the AlGaAs NWs exhibit two-mode behavior: GaAs- and AlAs-like modes which were exploited to determine the stoichiometry. Its dependence on the growth temperature was determined. The Raman spectra show two sets of GaAs- and AlAs-like modes indicating regions with different stoichiometries within a single NW. The composition gradient oft the NWs can be understood as the unintentional formation of a core-shell structure. Furthermore, the presence of coupled plasmon-LO phonon peaks in the spectra was related to (unintentional) doping of the NWs.