Abstract
A Raman scattering method is used to investigate structures containing nanosize GaAs and AlAs clusters, which were grown by molecular-beam epitaxy on InAs substrates by the mechanism of self-organized growth under mechanical stress. A large shift of the phonon lines of GaAs and AlAs clusters with respect to the phonon frequencies in the bulk materials (36 and 24 cm−1 for GaAs LO and TO phonons and 55 and 28 cm−1 for AlAs LO and TO phonons, respectively) is observed in the spectra. This fact is explained by the presence of strong mechanical stresses in the GaAs and AlAs clusters. A comparison of the experimental data with the computed strain dependences of the phonon frequencies shows that the GaAs and AlAs clusters are pseudomorphic, i.e., they do not contain dislocations, which lead to relaxation of the mechanical stresses. In the interval between the InAs TO and LO phonon frequencies, the Raman scattering spectra contain features associated with interfacial phonons. The position of these features also attests to the formation of three-dimensional GaAs and AlAs islands and are described well by a continuum dielectric model.
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Pis’ma Zh. Éksp. Teor. Fiz. 70, No. 7, 463–467 (10 October 1999)