Strain effects on optical phonons in 〈111〉 GaAs layers analyzed by Raman scattering

Abstract

Strain and thermal effects on longitudinal and transverse optical (LO) and (TO) phonon frequencies and on associated electron–phonon interactions have been analyzed in GaAs. We focus separately on these effects to treat each one thoroughly. By using lattice-mismatched 〈111〉 Si or CaF2 substrates, GaAs layers with highly tensile or compressive strain have been analyzed. We show that the LO/TO Raman scattering efficiency ratio, i.e., the electro-optic versus the atomic displacement electron-phonon mechanisms, varies with the built-in strain and hence its induced piezoelectric field. The Raman selection rules are valid in this process. The increase and decrease of this ratio compared to a reference suggest an interference effect. We discuss this phenomenon on the basis of strain-induced Raman scattering.