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Published online by Cambridge University Press: 28 March 2008
In this work, we study the optical interband transitions of InP on silicon (InP/Si) and on porous silicon (InP/PSi) substrates grown by molecular beam epitaxy (MBE). Spectroscopic ellipsometry for photon energies from 2 to 5 eV is used to determine the InP/Si and InP/PSi complex refractive index and thickness. Bruggeman effective medium approximation (EMA) associated to the Cauchy model are used to model the experimental ellipsometric data. We have found that the E 1 and E 1 + $\Delta _{1}$ transition energies of InP/Si and InP/PSi shift to low energies compared to bulk InP. This effect is interpreted as a result of the strain relaxation of the InP layers grown respectively on Si and porous Si substrates.