In this article we present results from a Raman scattering study of AlAs monolayers in GaAs grown by molecular beam epitaxy. A recent model for the LO phonons in AlxGa1-xAs developed by Molinari et al. [Appl. Surf. Sci. 56-58, 617 (1992); Phys. Rev. B 45. 4280 (1992)] gives excellent qualitative agreement with our measurements, We show that intermixing between AlAs and GaAs is reduced through the use of low substrate temperatures and migration-enhanced epitaxy. We show the utility of the LO phonon model for obtaining quantitative information about the Al concentration in a monolayer. We also discuss the utility of using Raman scattering to help determine the optimum growth conditions to minimize intermixing of GaAs/AlAs interfaces and for mapping Al flux variations across a sample.