STRAIN EFFECTS ON OPTICAL PHONONS IN (111)GAAS-LAYERS ANALYZED BY RAMAN-SCATTERING

Strain and thermal effects on longitudinal and transverse optical (LO) and (TO) phonon frequencies and on associated electron-phonon interac tions 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 strai n have been analyzed. We show that the LO/TO Raman scattering efficien cy ratio, i.e., the electro-optic versus the atomic displacement elect ron-phonon mechanisms, varies with the built-in strain and hence its i nduced piezoelectric field. The Raman selection rules are valid in thi s process. The increase and decrease of this ratio compared to a refer ence suggest an interference effect. We discuss this phenomenon on the basis of strain-induced Raman scattering. (C) 1997 American Institute of Physics. [S0021-8979(97)04721-X].