Spectroscopic ellipsometry (SE) from 0.8 to 5 eV and photoreflectance (PR) from 0.7 to 1.5 eV were used to study the interband optical response at room temperature of epitaxial GaAs1−xSbx layers with 0<x<0.5. The samples were grown by molecular-beam epitaxy at 520 °C on (001)-GaAs substrates and characterized by low-temperature photoluminescence and x-ray diffraction. The complex dielectric function (ω) of GaAs1−xSbx vs x was derived from the ellipsometric spectra after mathematically removing the oxide overlayer effects. The SE and PR spectra were analyzed with their energy derivatives in terms of standard analytical line shapes: in particular the E0, E1, E1+Δ1. E0′, and E2 critical point energies were derived as a function of x. On this basis the energy-shift model is appropriate to interpolate x(ω) for any x<0.5, thus allowing a nondestructive optical diagnostic of epitaxial heterostructures based on GaAs1−xSbx.
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