Phonon study of temperature evolution of strain in GaAs/Si(0 0 1) and GaAs/Si(1 1 1) 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.