Vibrational properties of isolated AlAs monolayers embedded in GaAs: a theoretical study of the effects of disorder

We present ab-initio calculations of Raman spectra of a prototype superlattice (SL) formed by the periodic repetition of an AlAs single monolayer embedded between two thicker GaAs layers. By comparing results for the ideal structure and for disordered configurations characterized by cationic intermixing, we demonstrate that AlAs-like longitudinal optical modes are extremely sensitive to disorder and may allow a quantitative characterization of the actual composition profiles obtained in real samples. The general implications of this conclusion for the study of interface intermixing in GaAs/AlAs SL's are discussed.