Raman and dielectric function spectra of strained GaAs1−xSbx layers on InP

Abstract

Raman spectroscopy and variable angle spectroscopic ellipsometry (SE) were used to study pseudomorphically strained GaAs1−xSbx 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 GaAs1−xSbx, 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 ωLO=292.3−51x(cm−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 GaAs1−xSbx dielectric function. From the resulting parametric dielectric functions the composition dependence of the E1 and E1+Δ1 critical point energies was deduced for pseudomorphically strained GaAs1−xSbx on InP and, after correction for strain effects on the interband transitions, also for unstrained GaAs1−xSbx.