RAMAN STUDIES ON GAAS EPITAXIAL-FILMS ON SI

Raman spectroscopy has been applied to the study of the effects of thermal expansion and lattice mismatch between GaAs and Si on the stress in GaAs films. The amount of stress in GaAs films of various thicknesses has been estimated from the GaAs LO phonon frequency and the half-width. By correcting the measured GaAs LO phonon frequency by using the spatial correlation (SC) model, it is shown that compressive stress exists in GaAs films due to accommodation of the lattice mismatch when the film is very thin. It has been also found that the compressive stress decreases with increased film thickness. The misfit dislocations at the GaAs/Si interface have been investigated by HR-TEM. The density of misfit dislocations increases with increased film thickness. The compressive stress in GaAs films due to accommodation of the lattice mismatch is released mainly by an increase of the density of misfit dislocations at the heterointerface as the film thickness increases.