Optical-phonon Raman-scattering study of short-period GaAs-AlAs superlattices: An examination of interface disorder

The effect of cation intermixing on the Raman spectrum of GaAs-AlAs superlattices has been investigated. Experimental measurements are compared with theoretical predictions based on fully three-dimensional supercell calculations. The accuracy of the modeled Raman spectra makes it possible to evaluate different mechanisms of interface disorder on a quantitative basis. In particular, a detailed comparison is made between the compositional profiles predicted by gallium-surface-segregation models and those resulting from simple cation intermixing at the GaAs-AlAs interfaces. Best agreement with experiment is obtained for the predictions of the surface-segregation models. These models, however, are unable to account simultaneously for the growth temperature dependence of the GaAs-like and AlAs-like Raman spectra, even when the kinetics of the disordering process is fully taken into account.