Phonon study of temperature evolution of strain in GaAs/Si (001)) and GaAs/Si (111) heterostructures

The temperature evolution of strain in GaAs layers grown on Si(0 0 1) and Si(1 1 1) substrates has been investigated by Raman scattering. The Raman results show that for temperatures lower than a certain temperature (?280 K for the (0 0 1) and ?400 K for (1 1 1) growth directions) the phonon modes for the epilayers shift toward lower frequencies in comparison to bulk material. This is due to the `thermal' strain arising from the difference in thermal expansion coefficients between GaAs epilayer and Si. A reverse phenomenon occurs at higher temperatures indicating the presence of compressive strain due to the mismatch in lattice constants between the GaAs epilayers and the Si substrate.