Raman scattering in InAs/AlGaAs quantum dot nanostructures

We report on Raman scattering experiments on InAs/AlxGa1−xAs quantum dot heterostructures with 0≤x≤0.6. The samples were prepared by using molecular beam epitaxy (MBE) and atomic layer MBE for the growth of different layers. For x>0, we detected several lines originating from the AlxGa1−xAs alloy. These can be related to scattering from GaAs-like and AlAs-like phonons with q≅0, and weaker scattering from disorder-activated phonons with q≠0. In particular, we identified a line at ∼250 cm−1 as due to disorder-activated longitudinal optical phonons in the alloy. This conclusion is different than the attribution of this line to scattering from dots and, consequently, we do not recognize the possibility of deriving any information about the actual composition of the dots from an analysis of this line as proposed by other authors.