Self-assembled islands in the (Ga,Al)As/InAs heteroepitaxial system studied by Raman spectroscopy

Phonon spectra of self-assembled GaAs and AlAs nanometer-sized islands in a n InAs matrix as well as InAs quantum dots embedded in AlAs were studied by Raman spectroscopy. Large strain-induced shifts of optical phonon lines of the islands from respective bulk values were observed. The experimental ph onon frequencies are characteristic of coherently strained dislocation-free islands. In InAs quantum dots embedded in AlAs the position of optical pho non lines in the Raman spectra was observed to depend on the excitation ene rgy. This behaviour is explained by the presence of smaller-sized dots in w hich the phonon confinement effect becomes significant. Doublets of folded acoustic phonons similar to those of planar superlattices are present in th e low-frequency Raman spectra of multilayer structures with AlAs and GaAs i slands embedded in InAs.