GaSb/GaAs heteroepitaxy characterized as a stress-free system

Thin layers of GaSb grown on GaAs by molecular beam epitaxy have been studied by Raman spectroscopy and transmission electron microscopy. In spite of the high value of the lattice mismatch (8%), these systems reveal a good crystalline quality: as a matter of fact, the lattice dynamics analysed through the resonant Raman scattering lead to a large correlation length for the optical modes. Moreover, they evidence the unstrained nature of the epilayers. The absence of the residual strain is connected to the highly regular network of Lomer dislocations observed by TEM. Obtaining such a perfect array of dislocations is a consequence of both the characteristic of the system (high lattice mismatch, same cationic sites) and the peculiar growth conditions (ideal surface preparation due to the buffer layer, adequate temperature allowing the direct relaxation of GaSb by island growth).