Optical functions of InGaP/GaAs epitaxial layers from 0.01 to 5.5 eV

摘要

In_(0.49)Ga_(0.51) P films, both undoped and doped n- and p-type (up to 10~(18) cm~(-3)), were grown lattice matched on GaAs substrates, with different miscut angles, by Metal-Organic Vapour Phase Epitaxy (MOVPE) at different temperatures. The shift of the fundamental gap E_0, caused by "ordering effect" was measured as a function of temperature by photoluminescence. The complex refractive index n-tilde = n + ik and the dielectric function ε-tilde = ε_1 + iε_2 at room temperature were determined from 0.01 to 5.5 eV by using complementary data from fast-Fourier-transform far-infrared (FFT-FIR), dispersive, and ellipsometric spectroscopies. The effect of the native oxide was accounted for and the self-consistency of the optical functions was checked in the framework of the Kramers-Kronig causality relations. In the restrahlen region the dielectric function was well fitted by classical Lorentz oscillators; in the transparent region below E_0, the refractive index was modelled by a Sellmeier dispersion relation; in the interband region the dielectric function was well reproduced by analytical lineshapes associated to seven critical points. Thus parametrized analytical expressions were obtained for the optical functions all over the spectral range, without discontinuities, to be used in the modelling and characterization of multi-layer structures, also on opaque substrates.