Raman and dielectric function spectra of strained GaAs(1-x)Sb(x) layers on InP

Raman spectroscopy and variable angle spectroscopic ellipsometry (SE) were used to study pseudomorphically strained GaAs(1-x)Sb(x) layers (0.22 <= x <= 0.65) grown on InP by metal-organic chemical vapor deposition. From the Raman spectra the composition dependence of the GaAs-like LO phonon mode was deduced. For comparison with literature data for unstrained GaAs(1-x)Sb(x), the strain-induced frequency shift of the GaAs-like LO phonon was calculated and subtracted from the present experimental data. When corrected for strain effects the composition dependent GaAs-like LO phonon frequency could be fitted by the linear relation omega(LO)=293,3-51x cm (exp -1) for the present range of alloy compositions. The pseudodielectric function spectra, deduced from SE measurements covering the range of photon energies from 0.8 to 5.0 eV, were fitted by a multilayer model employing a set of parametric oscillators to describe the GaAs(1-x)Sb(x) dielectric function. From the resulting parametric dielectric functions the composition dependence of the E(1) and E(1)+Delta(1) critical point energies was deduced for pseudomorphically strained GaAs(1-x)Sb(x) on InP and, after correction for strain effects on the interband transitions, also for unstrained GaAs(1-x)Sb(x).