Optical constants of In0.53Ga0.47As/InP: Experiment and modeling

Abstract

The optical constants ε(E)=ε1(E)+iε2(E) of unintentionally doped In0.53Ga0.47As lattice matched to InP have been measured at 300 K using spectral ellipsometry in the range of 0.4 to 5.1 eV. The ε(E) spectra displayed distinct structures associated with critical points at E0 (direct gap), spin-orbit split E0+Δ0 component, spin-orbit split E1, E1+Δ1, E0′ feature, as well as E2. The experimental data over the entire measured spectral range (after oxide removal) has been fit using the Holden model dielectric function [Holden et al., Phys. Rev. B 56, 4037 (1997)], plus a Kramers–Kronig consistent correction, described in this work, that improves the fitting at low energies. This extended model is based on the electronic energy-band structure near these critical points plus excitonic and band-to-band Coulomb-enhancement effects at E0, E0+Δ0, and the E1, E1+Δ1, doublet. In addition to evaluating the energies of these various band-to-band critical points, information about the binding energy (R1) of the two-dimensional exciton related to the E1, E1+Δ1 critical points was obtained. The value of R1 was in good agreement with effective mass/k⋅p theory. The ability to evaluate R1 has important ramifications for first-principles band-structure calculations that include exciton effects at E0, E1, and E2 [M. Rohlfing and S. G. Louie, Phys. Rev. Lett. 81, 2312 (1998); S. Albrecht et al., Phys. Rev. Lett. 80, 4510 (1998)].