Optical constants of In _0.53Ga _0.47As/InP: Experiment and modeling

Abstract

The optical constants ε(E)=ε 1(E) +iε 2(E) of unintentionally doped In 0.53Ga 0.47As 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 E 0 (direct gap), spin-orbit split E 0+Δ 0 component, spin-orbit split E 1, E 1+Δ 1, E 0′ feature, as well as E 2. 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 E 0, E 0+Δ 0, the E 1, E 1+Δ 1, doublet. In addition to evaluating the energies of these various band-to-band critical points, information about the binding energy (R 1) of the two-dimensional exciton related to the E 1, E 1+Δ 1 critical points was obtained. The value of R 1 was in good agreement with effective mass/kṡp theory. The ability to evaluate R 1 has important ramifications for first-principles band-structure calculations that include exciton effects at E 0, E 1, E 2 [M. Rohlfing and S. G. Louie, Phys. Rev. Lett. 81, 2312 (1998); S. Albrecht et al., Phys. Rev. Lett. 80, 4510 (1998)]. © 2002 American Institute of Physics. © 2002 American Institute of Physics.